Method for stabilizing a spinal segment

ABSTRACT

A surgical implant is provided that includes first and second abutment surfaces between which are positioned a force imparting mechanism. A sheath is positioned between the first and second abutment surfaces, and surrounds the force imparting mechanism. The sheath is fabricated from a material that accommodates relative movement of the abutment members, while exhibiting substantially inert behavior relative to surrounding anatomical structures. The sheath is generally fabricated from expanded polytetrafluoroethylene, ultra-high molecular weight polyethylene, a copolymer of polycarbonate and a urethane, or a blend of a polycarbonate and a urethane. The force imparting member may include one or more springs, e.g., a pair of nested springs. The surgical implant may be a dynamic spine stabilizing member that is advantageously incorporated into a spine stabilization system to offer clinically efficacious results.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application that claims thebenefit of a non-provisional patent application entitled “SurgicalImplant Devices and Systems Including a Sheath Member,” filed on Dec.31, 2004 and assigned Ser. No. 11/027,073 (now U.S. Pat. No. 7,027,475).In addition, the foregoing patent application is incorporated in itsentirety herein by reference to the extent not inconsistent herewith.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to advantageous methods and apparatus forspinal stabilization. More particularly, the present disclosure relatesto methods and apparatus for providing dynamic stabilization to thespine so as to provide clinically efficacious results.

2. Background Art

Low back pain is one of the most expensive diseases afflictingindustrialized societies. With the exception of the common cold, itaccounts for more doctor visits than any other ailment. The spectrum oflow back pain is wide, ranging from periods of intense disabling painwhich resolve to varying degrees of chronic pain. The conservativetreatments available for lower back pain include: cold packs, physicaltherapy, narcotics, steroids and chiropractic maneuvers. Once a patienthas exhausted all conservative therapy, the surgical options generallyrange from micro discectomy, a relatively minor procedure to relievepressure on the nerve root and spinal cord, to fusion, which takes awayspinal motion at the level of pain.

Each year, over 200,000 patients undergo lumbar fusion surgery in theUnited States. While fusion is effective about seventy percent of thetime, there are consequences even to these successful procedures,including a reduced range of motion and an increased load transfer toadjacent levels of the spine, which may accelerate degeneration at thoselevels. Further, a significant number of back-pain patients, estimatedto exceed seven million in the U.S., simply endure chronic low-backpain, rather than risk procedures that may not be appropriate oreffective in alleviating their symptoms.

New treatment modalities, collectively called motion preservationdevices, are currently being developed to address these limitations.Some promising therapies are in the form of nucleus, disc or facetreplacements. Other motion preservation devices provide dynamic internalstabilization of the injured and/or degenerated spine, e.g., the Dynesysstabilization system (Zimmer, Inc.; Warsaw, Ind.) and the Graf Ligament.A major goal of this concept is the stabilization of the spine toprevent pain while preserving near normal spinal function. The primarydifference in the two types of motion preservation devices is thatreplacement devices are utilized with the goal of replacing degeneratedanatomical structures which facilitate motion while dynamic internalstabilization devices are utilized with the goal of stabilizing andcontrolling abnormal spinal motion.

Over ten years ago a hypothesis of low back pain was presented in whichthe spinal system was conceptualized as consisting of the spinal column(vertebrae, discs and ligaments), the muscles surrounding the spinalcolumn, and a neuromuscular control unit which helps stabilize the spineduring various activities of daily living. Panjabi M M. “The stabilizingsystem of the spine. Part I. Function, dysfunction, adaptation, andenhancement.” J Spinal Disord 5 (4): 383-389, 1992a. A corollary of thishypothesis was that strong spinal muscles are needed when a spine isinjured or degenerated. This was especially true while standing inneutral posture. Panjabi M M. “The stabilizing system of the spine. PartII. Neutral zone and instability hypothesis.” J Spinal Disord 5 (4):390-397, 1992b. In other words, a low-back patient needs to havesufficient well-coordinated muscle forces, strengthening and trainingthe muscles where necessary, so they provide maximum protection whilestanding in neutral posture.

Dynamic stabilization (non-fusion) devices need certain functionality inorder to assist the compromised (injured or degenerated with diminishedmechanical integrity) spine of a back patient. Specifically, the devicesmust provide mechanical assistance to the compromised spine, especiallyin the neutral zone where it is needed most. The “neutral zone” refersto a region of low spinal stiffness or the toe-region of theMoment-Rotation curve of the spinal segment (see FIG. 1). Panjabi M M,Gael V K, Takata K. 1981 Volvo Award in Biomechanics. “PhysiologicalStrains in Lumbar Spinal Ligaments, an in vitro Biomechanical Study.”Spine 7 (3): 192-203, 1982. The neutral zone is commonly defined as thecentral part of the range of motion around the neutral posture where thesoft tissues of the spine and the facet joints provide least resistanceto spinal motion.

This concept may be visualized with reference to load-displacement ormoment-rotation curves for an intact spine and an injured spine, asshown in FIG. 1. The curves are non-linear; that is, the spinemechanical properties change with the amount of angulations and/orrotation. If the curves on the positive and negative sides areunderstood to represent spinal behavior in flexion and extension,respectively, then the slope of the curve at each point representsspinal stiffness. As seen in FIG. 1, the neutral zone is the lowstiffness region of the range of motion.

Experiments have shown that after an injury to the spinal column and/ordegeneration of the spine, neutral zones, as well as ranges of motion,increase (see FIG. 1). However, the neutral zone increases to a greaterextent than does the range of motion, when described as a percentage ofthe corresponding intact values. This implies that the neutral zone maybe a better measure of spinal injury and instability than the range ofmotion. Clinical studies have also found that range of motion does notcorrelate well with low back pain. Therefore, an unstable spine needs tobe stabilized, especially in the neutral zone.

With the foregoing in mind, those skilled in the art will understandthat a need exists for spinal stabilization devices, systems and/ormethods that overcome the shortcomings of prior art devices, systems andmethods. The present invention provides devices, systems and methods forenhanced and efficacious spinal stabilization. More particularly, thepresent disclosure provides advantageous dynamic internal stabilizationdevices, systems and methods that are flexible so as to move with thespine, thus allowing the disc, the facet joints, and the ligamentsnormal (or improved) physiological motion and loads necessary formaintaining their nutritional well-being. The devices, systems andmethods of the present disclosure also advantageously accommodatedifferent physical characteristics of individual patients and anatomiesto achieve a desired and/or improved posture for each individualpatient.

SUMMARY OF THE PRESENT DISCLOSURE

According to the present disclosure, advantageous devices, systems andmethods for spinal stabilization are provided. According to preferredembodiments of the present disclosure, the disclosed devices, systemsand methods provide dynamic stabilization to the spine so as to provideclinically efficacious results. In addition, the disclosed devices,systems and methods offer clinical advantages, including ease ofinstallation, versatility/flexibility in application, and superiorclinical results for individuals encountering lower back pain and otherspine-related difficulties.

According to exemplary implementations of the present disclosure,devices, systems and methods are provided that encompass one or morepedicle screws for attachment to spinal structures. The pedicle screw(s)of the present disclosure are typically employed as part of a spinestabilization system that includes one or more of the followingadvantageous structural and/or functional attributes:

-   -   A dynamic junction between at least one pedicle screw and at        least one elongated member (or multiple elongated members),        e.g., rod(s), that engage and/or otherwise cooperate with the        pedicle screw;    -   Advantageous assembly mechanisms that facilitate        assembly/installation of a ball/sphere or other accessory        component relative to the pedicle screw and provide advantageous        functional attributes as part of a spinal stabilization system.        Exemplary mechanisms include advantageous collet-based        mechanisms, cooperatively threaded mechanisms, mechanisms that        apply bearing forces against a ball/sphere or other accessory        component, and/or mechanisms that include a snap ring or        analogous structure;    -   Advantageous multi-level dynamic spine stabilization        systems/implementations, including multi-level systems that        permit one or more adjustments to be made (e.g., in situ and/or        prior to clinical installation), e.g., adjustments as to the        magnitude and/or displacement-response characteristics of the        forces applied by the stabilization system; according to        exemplary multi-level implementations of the present disclosure,        different stabilization modalities may be employed at individual        stabilization levels, e.g., by mixing of dynamic and non-dynamic        stabilizing structures between adjacent pedicle screws at        different stabilization levels;    -   Advantageous installation accessories (e.g., cone structures)        for facilitating placement/installation of spine stabilization        system components, such accessories being particularly adapted        for use with conventional guidewire(s) to facilitate        alignment/positioning of system components relative to the        pedicle screw;    -   Dynamic stabilization systems and/or other surgical implants        that include a cover and/or sheath structure that provides        advantageous protection to inner force-imparting component(s),        e.g., one or more springs, while exhibiting clinically        acceptable interaction with surrounding anatomical fluids and/or        structures, e.g., a cover and/or sheath structure that is        fabricated (in whole or in part) from ePTFE, UHMWPE and/or        alternative polymeric materials such as        polycarbonate-polyurethane copolymers and/or blends;    -   Advantageous dynamic spine stabilization connection systems that        facilitate substantially rigid attachment of an elongated member        (e.g., a rod) relative to the pedicle screw while simultaneously        facilitating movement relative to adjacent structures (e.g., an        adjacent pedicle screw) to permit easy and efficacious        intra-operative system placement;    -   An advantageous “pre-load” arrangement for a securing structure        (e.g., a set screw) that may be used in situ to mount a ball        joint or other accessory component relative to the pedicle        screw, thereby minimizing the potential for clinical        difficulties associated with location and/or alignment of such        securing structure(s).

As noted above, advantageous spine stabilization devices, systems andmethods may incorporate one or more of the foregoing structural and/orfunctional attributes. Thus, it is contemplated that a system, deviceand/or method may utilize only one of the advantageousstructures/functions set forth above, a plurality of the advantageousstructures/functions described herein, or all of the foregoingstructures/functions, without departing from the spirit or scope of thepresent disclosure. Stated differently, each of the structures andfunctions described herein is believed to offer benefits, e.g., clinicaladvantages to clinicians and/or patients, whether used alone or incombination with others of the disclosed structures/functions.

Generally, the structures/functions of the threaded shaft portions ofthe pedicle screws disclosed herein are of conventional design. Thus,installation of the pedicle screws is generally undertaken by aclinician in a conventional manner. Selection and placement of thepedicle screws is generally based on conventional criteria, as are knownto persons skilled in the art. However, unlike conventionalpedicle-screw based systems, the devices, systems, and methods of thepresent disclosure offer advantageous clinical results, e.g., based onease and flexibility of rod/elongated member placement, dynamicattributes of the rod/elongated member in situ relative to the pediclescrews, and/or dynamic force delivery in response to spinal displacementstimulus.

Additional advantageous features and functions associated with thedevices, systems and methods of the present disclosure will be apparentto persons skilled in the art from the detailed description whichfollows, particularly when read in conjunction with the figures appendedhereto. Such additional features and functions, including the structuraland mechanistic characteristics associated therewith, are expresslyencompassed within the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of ordinary skill in the art in making and using thedisclosed devices, systems and methods for spinal stabilization andother applications, reference is made to the appended figures wherein:

FIG. 1 is a Moment-Rotation curve for a spinal segment (intact andinjured), showing relatively low spinal stiffness within the neutralzone.

FIG. 2 is a schematic representation of a spinal segment in conjunctionwith a Moment-Rotation curve for a spinal segment, showing relativelylow spinal stiffness within the neutral zone.

FIG. 3 a is a schematic representation of an exemplary device/systemaccording to the present disclosure in conjunction with aForce-Displacement curve, demonstrating increased resistance providedwithin the central zone of a dynamic spine stabilizer according to thepresent disclosure.

FIG. 3 b is a Force-Displacement curve demonstrating a change in profileachieved through replacement of springs according to an exemplaryembodiment of the present disclosure.

FIG. 3 c is a posterior or dorsal view of the spine with a pair ofexemplary stabilizers secured thereto.

FIG. 3 d is a lateral or side view showing an exemplary stabilizeraccording to the present disclosure in tension.

FIG. 3 e is a lateral or side view showing an exemplary stabilizeraccording to the present disclosure in compression.

FIG. 4 is a schematic representation of an exemplary dynamic spinestabilizer according to the present disclosure.

FIG. 5 is a schematic representation of an alternate exemplaryembodiment of a dynamic spine stabilizer in accordance with one aspectof the present disclosure.

FIG. 6 is a Moment-Rotation curve demonstrating the manner in which anexemplary dynamic spine stabilizer according to the present disclosureassists spinal stabilization.

FIGS. 7 a and 7 b are, respectively, a free body diagram of an exemplarydynamic stabilizer according to the present disclosure and a diagramrepresenting the central zone of such exemplary stabilizer.

FIG. 8 is an exploded view of an exemplary dynamic spine stabilizationsystem in accordance with an embodiment of the present disclosure.

FIG. 9 is a perspective view of the exemplary dynamic spinestabilization system shown in FIG. 8.

FIGS. 10 and 11 are perspective views showing exemplary attachmentmembers for use with dynamic spine stabilizations of the presentdisclosure.

FIG. 12 is a schematic representation showing a guidewire assemblytechnique in accordance with an exemplary implementation of the spinestabilization techniques of the present disclosure.

FIG. 13 is a schematic side view of a pair of pedicle screws accordingto an exemplary embodiment of the present disclosure.

FIG. 14 is a side view of a pair of pedicle screws in combination withguidewire assemblies according to an exemplary embodiment of the presentdisclosure.

FIG. 15 a is a perspective view of an attachment member that is adaptedto facilitate alignment with elongated member(s), e.g., rod(s),according to exemplary embodiments of the present disclosure.

FIG. 15 b is a side view of a spherical element for use in an attachmentmember according to an exemplary embodiment of the present disclosure.

FIG. 16 is a top view of a pair of single level spinal stabilizationsystems according to an exemplary embodiment of the present disclosure.

FIG. 17 is an illustrative Force-Displacement curve for an exemplarydynamic spine stabilization system according to the present disclosure.

FIG. 18 is a schematic top view of an exemplary multiple level, dynamicspine stabilization system in accordance with an implementation of thepresent disclosure.

FIG. 19 is a schematic, exploded side view of a portion of the exemplarydynamic spine stabilization system of FIG. 18.

FIG. 20 is a schematic side view of an aspect of the exemplary dynamicspine stabilization system of FIG. 18.

FIG. 21 is a perspective view of the exemplary multiple level, dynamicspine stabilization system of FIGS. 18 to 20.

FIG. 22 is a further perspective view of the exemplary multiple level,dynamic spine stabilization system of FIG. 19.

FIG. 23 is a side view of exemplary portions of a pedicle screw/balljoint subassembly (partially exploded) according to the presentdisclosure.

FIGS. 24 a, 24 b and 24 c are views of an alternative collet-basedmechanism according to the present disclosure;

FIGS. 25 a, 25 b and 25 c are views of a non-spreading collet-basedmechanism according to the present disclosure;

FIGS. 26 a, 26 b and 26 c are views of a further alternative mechanismfor mounting a ball/sphere relative to a pedicle screw according to thepresent disclosure;

FIG. 27 is a cross-sectional side view an additional alternativemechanism for mounting a ball/sphere relative to a pedicle screwaccording to the present disclosure.

FIG. 28 is a perspective view of an exemplary socket member and springcap according to an exemplary embodiment of the present disclosure.

FIG. 29 is an exploded view of an alternative dynamic junction between apedicle screw and accessory component(s) according to the presentdisclosure.

FIG. 30 is a perspective view of a spring cap rod according to anexemplary embodiment of the present disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present disclosure provides advantageous devices, systems andmethods for spinal stabilization and/or alternative surgical implantapplications. More particularly, the present disclosure providesdevices, systems and methods that deliver dynamic stabilization to thespine so as to provide clinically efficacious results. The exemplaryembodiments disclosed herein are illustrative of the advantageous spinestabilization systems and surgical implants of the present disclosure,and methods/techniques for implementation thereof. It should beunderstood, however, that the disclosed embodiments are merely exemplaryof the present invention, which may be embodied in various forms.Therefore, the details disclosed herein with reference to exemplarydynamic spinal stabilization systems and associated methods/techniquesare not to be interpreted as limiting, but merely as the basis forteaching one skilled in the art how to make and/or use the advantageousdynamic spinal stabilization systems and alternative surgical implantsof the present disclosure.

With reference to FIGS. 2, 3 a-e and 4, an exemplary method andapparatus for spinal stabilization are disclosed. Although thedescription which follows is primarily directed to spinal stabilization,it is expressly contemplated that the disclosed methods and apparatusmay be advantageously employed in alternative surgical applications,e.g., any long bone application. Thus, throughout the detaileddisclosure which follows, it is to be understood that references andteachings with respect to spinal stabilization are merely illustrativeand that the disclosed systems, devices and methods find application ina multitude of a surgical/anatomical settings, including specificallylong bone applications involving the femur, tibia, fibula, ulna, and/orhumerus.

In accordance with an exemplary embodiment of the present disclosure,the spinal stabilization method is achieved by securing an internaldynamic spine stabilizing member 10 between adjacent vertebrae 12, 14,thereby providing mechanical assistance in the form of elasticresistance to the region of the spine to which the dynamic spinestabilizing member 10 is attached. The elastic resistance is applied asa function of displacement such that greater stiffness, i.e., greaterincremental resistance, is provided while the spine is in its neutralzone and lesser mechanical stiffness, i.e., lesser incrementalresistance, is provided while the spine bends beyond its neutral zone.Although the term elastic resistance is generally used throughout thebody of the present specification, other forms of resistance may beemployed without departing from the spirit of the present invention.

As those skilled in the art will certainly appreciate, and as mentionedabove, the “neutral zone” is understood to refer to a region of lowspinal stiffness or the toe-region of the Moment-Rotation curve of thespinal segment (see FIG. 2). That is, the neutral zone may be consideredto refer to a region of laxity around the neutral resting position of aspinal segment where there is minimal resistance to inter-vertebralmotion. The range of the neutral zone is considered to be of majorsignificance in determining spinal stability. Panjabi, M M. “Thestabilizing system of the spine. Part II. Neutral zone and instabilityhypothesis.” J Spinal Disorders 1992; 5(4): 390-397.

In fact, Dr. Panjabi (a presently named inventor) has previouslydescribed the load displacement curve associated with spinal stabilitythrough the use of a “ball in a bowl” analogy. According to thisanalogy, the shape of the bowl indicates spinal stability. A deeper bowlrepresents a more stable spine, while a more shallow bowl represents aless stable spine. Dr. Panjabi previously hypothesized that for someonewithout spinal injury there is a normal neutral zone (that part of therange of motion where there is minimal resistance to inter-vertebralmotion) with a normal range of motion and, in turn, no spinal pain. Inthis instance, the bowl is not too deep nor too shallow. However, whenan injury occurs to an anatomical structure associated with the spine,the neutral zone of the spinal column increases and “the ball” movesfreely over a larger distance. By the noted analogy, the bowl would beshallower and the ball less stable; consequently, pain would result fromthe enlarged neutral zone.

In general, pedicle screws 16, 18 are used to attach the dynamic spinestabilizing member 10 to the vertebrae 12, 14 of the spine usingwell-tolerated and familiar surgical procedures known to those skilledin the art. The pedicle screws 16, 18 in combination with a dynamicspine stabilizing member 10 comprise a stabilizing system 11. Inaccordance with an exemplary embodiment, and as those skilled in the artwill certainly appreciate, paired stabilizing systems 11 are commonlyused to balance the loads applied to the spine (see FIG. 3 c). Thedynamic spine stabilizing members 10 assist the compromised (injuredand/or degenerated) spine of a back-pain patient, and help her/himperform daily activities. The dynamic spine stabilizing member 10 doesso as part of stabilizing system 11 by providing controlled resistanceto spinal motion, particularly around neutral posture in the region ofneutral zone. As the spine bends forward (flexion) the stabilizingmember 10 is tensioned (see FIG. 3 d) and when the spine bends backward(extension) the stabilizing member 10 is compressed (see FIG. 3 e).

The resistance to displacement provided by the dynamic spine stabilizingmember 10 is non-linear, being greatest in its central zone so as tocorrespond to the individual's neutral zone; that is, the central zoneof the stabilizing member 10 provides a high level of mechanicalassistance in supporting the spine. As the individual moves beyond theneutral zone, the increase in resistance decreases to a more moderatelevel. As a result, the individual encounters greater resistance tomovement (or greater incremental resistance) while moving within theneutral zone.

The central zone of the dynamic spine stabilization system 11, that is,the range of motion in which the spine stabilization system 11 providesthe greatest incremental resistance to movement, may be adjustable atthe time of surgery according to exemplary embodiments of the presentdisclosure to suit the neutral zone of each individual patient. Thus,according to exemplary embodiments of the present disclosure, theresistance to movement provided by the dynamic spine stabilizing member10 is adjustable pre-operatively and/or intra-operatively. Thisadjustability helps to tailor the mechanical properties of the dynamicspine stabilizing system 11 to suit the compromised spine of theindividual patient. In addition, according to exemplary embodiments ofthe present disclosure, the length of the dynamic spine stabilizer 10may also (or alternatively) be adjustable intra-operatively to suitindividual patient anatomy and to achieve desired spinal posture. Insuch exemplary embodiments, the dynamic spine stabilizing element 10 canbe re-adjusted post-operatively with a surgical procedure to adjust itscentral zone, e.g., to accommodate a patient's altered needs.

With reference to FIG. 4, ball joints 36, 38 may be employed accordingto exemplary embodiments of the present disclosure to link or otherwisejoin the dynamic spine stabilizing member 10 with pedicle screws 16, 18.The junction of the dynamic spine stabilizing member 10 and pediclescrews 16, 18 is free and rotationally unconstrained. Thus, threerotational degrees of freedom are provided by advantageous dynamicjunctions according to the present disclosure. Alternative structuralarrangements are contemplated to provide the desired rotational degreesof freedom of the disclosed dynamic joints, e.g., universal jointstructures of the type disclosed in FIG. 29 and discussed herein below.The structures mounted with respect to the pedicle screw that support oraccommodate motion relative to the pedicle screw, e.g., the disclosedspherical elements and universal joint mechanisms, are exemplary motioninterface elements according to the present disclosure. Therefore, firstof all, by providing the dynamic junctions of the present disclosure,the spine is allowed all physiological motions of bending and twistingand, second, the dynamic spine stabilizing member 10 and pedicle screws16, 18 are protected from potentially harmful bending and/or torsionalforces, or moments. As previously stated, while ball joints aredisclosed in accordance with an exemplary embodiment of the presentdisclosure, the present disclosure is not limited to use of one or moreball joints, and other linking structures/mechanisms may be utilizedwithout departing from the spirit or scope of the present disclosure.

As there are ball joints 36, 38 mechanically cooperating with each endof the stabilizing member 10 according to the exemplary embodiment ofFIG. 4, bending moments are generally not transferred from the spine tothe stabilizing member 10 within stabilizing system 11. Further, it isimportant to recognize that the only forces associated with operation ofstabilizing member 10 are the forces due to the forces of springs 30, 32that form part of stabilizing member 10. These forces are solelydependent upon the tension and/or compression of the stabilizing member10 as determined by spinal motion. In summary, the forces associatedwith operation of stabilizing member 10 are limited to the springforces. Irrespective of the large loads on the spine, such as when aperson carries or lifts a heavy load, the loads experienced bystabilizing member 10 are only associated with the spring forcesdeveloped within stabilizing member 10, which are the result of spinalmotion and not the result of the spinal load. The stabilizing member 10is, therefore, uniquely able to assist the spine without enduring thehigh loads of the spine, allowing a wide range of design options.

The loading of the pedicle screws 16, 18 in the presently disclosedstabilizing system 11 is also quite different from that in prior artpedicle screw fixation devices. The only load experienced by the pediclescrews 16, 18 of stabilizing system 11 is the force delivered by thestabilizing member 10 which translates into pure axial force at the balljoint-screw interface. The design and operation of the disclosedstabilizing system 11 thus greatly reduces the bending moments placedonto pedicle screws 16, 18, as compared to prior art pedicle screwfusion systems. Due to the free motion associated with ball joints 36,38, the bending moment within each pedicle screw 16, 18 is theoreticallyzero at ball joints 36, 38, respectively, and the potential for failureis therefore advantageously reduced. In sum, the pedicle screws 16, 18,when used as part of the exemplary dynamic spine stabilization systemsof the present disclosure, early significantly less load and are placedunder significantly less stress than typical pedicle screws.

In FIG. 2, the Moment-Rotation curve for a healthy spine is shown inconfigurations with an exemplary stabilizing member 10 as part of adynamic spine stabilizing system. This curve shows the low resistance tomovement encountered in the neutral zone of a healthy spine. However,when the spine is injured, this curve changes and the spine becomesunstable, as evidenced by the expansion of the neutral zone (see FIG.1).

In accordance with exemplary embodiments of the present disclosure,people suffering from spinal injuries are best treated through devices,systems and methods that provide increased mechanical assistance in theneutral zone. As the spine moves beyond the neutral zone, the necessarymechanical assistance decreases and becomes more moderate. Inparticular, and with reference to FIG. 3 a, an exemplary support profilecontemplated through implementation of advantageously disclosed devices,systems and methods is depicted.

Three different profiles are shown in FIG. 3 a. The disclosed profilesare merely exemplary and demonstrate the possible support requirementswithin the neutral zone. Profile 1 is exemplary of an individualrequiring great assistance in the neutral zone and the central zone ofthe stabilizing system of the present disclosure is therefore increased,providing a high level of resistance over a great displacement; Profile2 is exemplary of an individual where less assistance is required in theneutral zone and the central zone of the stabilizing system of thepresent disclosure is therefore more moderate, providing increasedresistance over a more limited range of displacement; and Profile 3 isexemplary of situations where only slightly greater assistance isrequired in the neutral zone and the central zone of the stabilizingsystem of the present disclosure may therefore be decreased to provideincreased resistance over even a smaller range of displacement.

As those skilled in the art will certainly appreciate, the mechanicalassistance required and the range of the neutral zone will vary fromindividual to individual. However, the basic tenet of the presentinvention remains; that is, greater mechanical assistance for thoseindividuals suffering from spinal instability is required within theindividual's neutral zone. This assistance is provided in the form ofgreater resistance to movement provided within the neutral zone of theindividual and the central zone of the dynamic spine stabilizing member10 which advantageously forms part of a dynamic spine stabilizingsystem.

Exemplary dynamic spine stabilizing member 10 of the present disclosureadvantageously provides mechanical assistance in accordance with thedesired support profile. Further, exemplary embodiments of dynamic spinestabilizing member 10 provide for adjustability, e.g., via a concentricspring design. More specifically and with reference to exemplaryembodiments of the present disclosure, spine stabilizing system 10provides assistance to the compromised spine in the form of increasedstiffness, i.e., greater incremental resistance to movement (provided bysprings in accordance with a preferred embodiment) as the spine movesfrom the neutral posture, in any physiological direction. As mentionedabove, the Force-Displacement relationship provided by exemplarystabilizing system 10 and dynamic spine stabilizing member 10 arenon-linear, with greater incremental resistance around the neutral zoneof the spine and central zone of the stabilizing system 11, anddecreasing incremental resistance beyond the central zone of the dynamicspine stabilizing system 11 as the individual moves beyond the neutralzone (see FIG. 3 a).

The relationship of the present stabilizing system 11 to forces appliedduring tension and compression is further shown with reference to FIG. 3a. As discussed above, the behavior of the present stabilizing system 11is non-linear. The Load-Displacement curve has three zones: tension,central and compression. If K1 and K2 define the stiffness values in thetension and compression zones, respectively, the advantageousstabilizing systems according to the present disclosure are designedsuch that high stiffness is delivered in the central zone, i.e.,“K1+K2”. Depending upon the “preload” of stabilizing member 10, asdiscussed below in greater detail, the width of the central zone and,therefore, the region of high stiffness, can be adjusted.

With reference to FIG. 4, an exemplary dynamic spine stabilizing system11 that includes a dynamic spine stabilizing member 10 in accordancewith the present disclosure is schematically depicted. Dynamic spinestabilizing system 11 includes a support assembly associated with spinestabilizing member 10 in the form of a housing 20 composed of a firsthousing member 22 and a second housing member 24. The first housingmember 22 and the second housing member 24 are telescopically connectedvia external threads formed upon the open end 26 of the first housingmember 22 and internal threads formed upon the open end 28 of the secondhousing member 24. In this way, the housing 20 is completed by screwingthe first housing member 22 into the second housing member 24. As such,and as will be discussed below in greater detail, the relative distancebetween the first housing member 22 and the second housing member 24 canbe readily adjusted for the purpose of adjusting the compression offirst spring 30 and second spring 32 contained within the housing 20.Although springs are employed in accordance with a preferred embodimentof the present invention, other elastic members may be employed withoutdeparting from the spirit or scope of the present invention. A pistonassembly 34 links the first spring 30 and the second spring 32 relativeto first and second ball joints 36, 38. The first and second ball joints36, 38 are in turn shaped and designed for selective attachment topedicle screws 16, 18, which may extend from the respective vertebrae12, 14 (as shown, e.g., in FIG. 2).

The first ball joint 36 is secured relative to the closed end 39 of thefirst housing member 22 via a threaded engagement member 40 that isshaped and dimensioned for coupling with first housing member 22.According to an exemplary embodiment of the present disclosure, anaperture 42 is formed in the closed end 39 of the first housing member22 and is provided with threads for engaging the threaded portion ofengagement member 40. In this way, the first ball joint 36 substantiallycloses off the closed end 39 of the first housing member 22. The lengthof dynamic spine stabilizing system 11 may be readily adjusted byrotating the first ball joint 36 relative to first housing member 22 toadjust the extent of overlap between the first housing member 22 and theengagement member 40 of the first ball joint 36, i.e., the degree towhich engagement member 40 is nested within first housing member 22. Asthose skilled in the art will certainly appreciate, a threadedengagement between the first housing member 22 and the engagement member40 of the first ball joint 36 is disclosed in accordance with anexemplary embodiment of the present disclosure, although other couplingstructures (e.g., welding attachment, a bayonet lock or the like) may beemployed without departing from the spirit or scope of the presentinvention.

In an exemplary embodiment of the present disclosure, the closed end 44of the second housing member 24 is provided with a cap 46 having anaperture 48 formed therein. As will be discussed below in greaterdetail, the aperture 48 is shaped and dimensioned to accommodate passageof a piston rod 50 associated with piston assembly 34 therethrough.Exemplary piston assembly 34 includes a piston rod 50; first and secondsprings 30, 32; and retaining rods 52. The piston rod 50 includes a stopnut 54 and an enlarged head 56 at its first end 58. The enlarged head 56is rigidly connected to the piston rod 50 and includes guide holes 60through which the retaining rods 52 extend during operation of thepresent dynamic spine stabilizing member 10. As such, the enlarged head56 is guided along the retaining rods 52 while the second ball joint 38moves toward and away from the first ball joint 36, i.e., in connectionwith relative motion between first and second ball joints 36, 38. Aswill be discussed below in greater detail, the enlarged head 56interacts with the first spring 30 to create resistance as the dynamicspine stabilizing member 10 is extended and the spine is moved inflexion.

A stop nut 54 is fit over the piston rod 50 for free movement relativethereto. However, movement of the stop nut 54 toward the first balljoint 36 is prevented by the retaining rods 52 that support the stop nut54 and prevent the stop nut 54 from moving toward the first ball joint36. As will be discussed below in greater detail, the stop nut 54interacts with the second spring 32 to create resistance as the dynamicspine stabilizing member 10 is compressed and the spine is moved inextension.

The second end 62 of the piston rod 50 extends from the aperture 48 atthe closed end 44 of the second housing member 24, and is attached to anengagement member 64 associated with the second ball joint 38. In anexemplary embodiment of the present disclosure, the second end 62 of thepiston rod 50 is coupled to the engagement member 64 of the second balljoint 38 via a threaded engagement. As those skilled in the art willcertainly appreciate, a threaded engagement between the second end 62 ofthe piston rod 50 and the engagement member 64 of the second ball joint38 is disclosed in accordance with an exemplary embodiment, althoughother coupling structures may be employed without departing from thespirit or scope of the present invention.

As briefly mentioned above, first and second springs 30, 32 are held orcaptured within housing 20. In particular, the first spring 30 extendsbetween the enlarged head 56 of the piston rod 50 and the cap 46 of thesecond housing member 24. The second spring 32 extends between thedistal end of the engagement member 64 of the second ball joint 38 andthe stop nut 54 of the piston rod 50. A preloaded force applied by thefirst and second springs 30, 32 generally holds the piston rod in astatic position within the housing 20, and the piston rod 50 is able tomove relative to housing 20 during either extension or flexion of thespine.

In use, when the vertebrae 12, 14 are moved in flexion and the firstball joint 36 is drawn away from the second ball joint 38, i.e., thereis relative motion between first and second ball joints 36, 38 such thatthey are moving away from each other, the piston rod 50 is pulled withinthe housing 24 against the force being applied by the first spring 30.In particular, the enlarged head 56 of the piston rod 50 is moved towardthe closed end 44 of the second housing member 24. This movement causescompression of the first spring 30, creating resistance to the movementof the spine. With regard to the second spring 32, the second spring 32moves with the piston rod 50 away from second ball joint 38. As thevertebrae move in flexion within the neutral zone, the height of thesecond spring 32 is increased, reducing the distractive force, and ineffect increasing the resistance of the device to movement. Through thismechanism, as the spine moves in flexion from the initial position bothspring 30 and spring 32 resist the distraction of the device directly,either by increasing the load within the spring (i.e. first spring 30)or by decreasing the load assisting the motion (i.e. second spring 32).

However, when the spine is in extension, and the second ball joint 38 ismoved toward the first ball joint 36, the engagement member 64 of thesecond ball joint 38 moves toward the stop nut 54, which is held inplace by the retaining rods 52 as the piston rod 50 moves toward thefirst ball joint 36. This movement causes compression of the secondspring 32 held between the engagement member 64 of the second ball joint38 and the stop nut 54, to create resistance to the movement within thedynamic spine stabilizing member 10. With regard to the first spring 30,the first spring 30 is supported between the cap 46 and the enlargedhead 56, and as the vertebrae move in extension within the neutral zone,the height of the second spring 30 is increased, reducing thecompressive force, and in effect increasing the resistance of the deviceto movement. Through this mechanism, as the spine moves in extensionfrom the initial position both spring 32 and spring 30 resist thecompression of the device directly, either by increasing the load withinthe spring (i.e. second spring 32) or by decreasing the load assistingthe motion (i.e. first spring 30).

Based upon the use of two concentrically positioned elastic springs 30,32 as disclosed in accordance with an exemplary embodiment of thepresent invention, an assistance (force) profile as shown in FIG. 2 isprovided by the present dynamic spine stabilizing member 10. That is,the first and second springs 30, 32 work in conjunction to provide alarge elastic force when the dynamic spine stabilizing member 10 isdisplaced within the central zone of the stabilizing system 11. However,once displacement between the first ball joint 36 and the second balljoint 38 extends beyond the central zone of the stabilizing system 11and the neutral zone of the individual's spinal movement, theincremental resistance to motion is substantially reduced as theindividual no longer requires the substantial assistance needed withinthe neutral zone. This is accomplished by setting the central zone ofthe device disclosed herein. The central zone of the force displacementcurve is the area of the curve, which represents when both springs areacting in the device as described above. When the motion of the spine isoutside the neutral zone and the correlating device elongation orcompression is outside the set central zone, the spring, which iselongating, reaches its free length. Free length, as anybody skilled inthe art will appreciate, is the length of a spring when no force isapplied. In the advantageous, exemplary mechanism of the presentdisclosure, the resistance to movement of the device outside the centralzone (where both springs are acting to resist motion) is only reliant onthe resistance of one spring: either spring 30 in flexion or spring 32in extension.

As briefly discussed above, exemplary dynamic spine stabilizing member10 may be adjusted by rotation of the first housing member 22 relativeto the second housing member 24. This movement changes the distancebetween the first housing member 22 and the second housing member 24 ina manner which ultimately changes the preload placed across the firstand second springs 30, 32. This change in preload alters the resistanceprofile of the present dynamic spine stabilizing member 10 from thatshown in Profile 2 of FIG. 3 a to an increase in preload (see Profile 1of FIG. 3 a), which enlarges the effective range in which the first andsecond springs 30, 32 act in unison. This increased width of the centralzone of the stabilizing member 10 correlates to higher stiffness over alarger range of motion of the spine. This effect can be reversed, as isevident in Profile 3 of FIG. 3 a.

The present dynamic spine stabilizing member 10 is attached to pediclescrews 16, 18 extending from the vertebral section requiring support.During surgical attachment of the dynamic spine stabilizing member 10,the magnitude of the stabilizer's central zone can be adjusted for eachindividual patient according to exemplary embodiments of the presentdisclosure, as judged by the surgeon and/or quantified by an instabilitymeasurement device. This adjustable feature of the dynamic spinestabilizing member 10 is exemplified in the three explanatory profilesthat have been generated in accordance with an exemplary embodiment ofthe present invention (see FIGS. 3 a and 3 b; note the width of thedevice central zones).

Pre-operatively, the first and second elastic springs 30, 32 of thedynamic spine stabilizing member 10 can be replaced by a different setof springs (in whole or in part) to accommodate a wider range of spinalinstabilities. As expressed in FIG. 3 b, Profile 2 b demonstrates theforce displacement curve generated with a stiffer set of springs whencompared with the curve shown in Profile 2 a of FIG. 3 b.

Intra-operatively, the length of exemplary dynamic spine stabilizingmember 10 may be adjustable, e.g., by turning engagement member 40 ofthe first ball joint 36 to lengthen the stabilizing member 10 in orderto accommodate different patient anatomies and desired spinal posture.Pre-operatively, the piston rod 50 may be replaced with piston rods ofdiffering lengths/geometries to accommodate an even wider range ofanatomic variation.

The exemplary dynamic spine stabilizing member 10 disclosed herein hasbeen tested alone for its load-displacement relationship. When applyingtension, the dynamic spine stabilizing member 10 demonstrated increasingresistance up to a pre-defined displacement, followed by a reduced rateof increasing resistance until the device reached its fully elongatedposition. When subjected to compression, the dynamic spine stabilizingmember 10 demonstrated increasing resistance up to a pre-defineddisplacement, followed by a reduced rate of increasing resistance untilthe device reached its fully compressed position. Therefore, the dynamicspine stabilizing member 10 exhibits a load-displacement curve that isnon-linear with the greatest resistance to displacement offered aroundthe neutral posture. This advantageous behavior helps to normalize theload-displacement curve of a compromised spine.

In another exemplary embodiment of the present disclosure, withreference to FIG. 5, the stabilizing member 110 may be constructed withan in-line spring arrangement. In accordance with this embodiment, thehousing 120 is composed of first and second housing members 122, 124which are coupled with threads allowing for adjustability. A first balljoint 136 extends from or relative to the first housing member 122. Thesecond housing member 124 is provided with an aperture 148 through whichthe second end 162 of piston rod 150 extends. The second end 162 of thepiston rod 150 is attached relative to the second ball joint 138. Forexample, the second ball joint 138 may be screwed onto the piston rod150.

The piston rod 150 includes an enlarged head 156 at its first end 158.The first and second springs 130, 132 are respectively secured betweenthe enlarged head 156 and the closed ends 139, 144 of the first andsecond housing members 122, 124. In this way, the stabilizing member 110provides resistance to both expansion and compression using the samemechanical principles described for the previous embodiment, i.e.,stabilizing member 10.

Adjustment of the resistance profile in accordance with this alternateembodiment may be achieved by rotating the first housing member 122relative to the second housing member 124. Rotation in this way altersthe central zone of high resistance provided by stabilizing member 110.As previously described, one or both springs may also be exchanged tochange the slope of the force-displacement curve in two or three zones,respectively.

To explain how the exemplary stabilizing members 10, 110 assist acompromised spine (increased support in the neutral zone), reference ismade to the moment-rotation curves (FIG. 6). Four curves are shown: 1.Intact, 2. Injured, 3. Stabilizer (“DSS”) and, 4. Injured+Stabilizer(“DSS”). These are, respectively, the Moment-Rotation curves of theintact spine, injured spine, stabilizer alone, and stabilizer plusinjured spine. Of note, the latter curve (i.e., injured spine plusstabilizing system of the present disclosure) is close to the intactcurve. Thus, the stabilizer/stabilizing system of the presentdisclosure, which provides greater resistance to movement around theneutral posture, is well suited to compensate for the instability of thespine.

With reference to FIGS. 8 to 17, further embodiments of the advantageousstabilizing system 211 of the present disclosure (and associated forceprofile characteristics) are schematically depicted and describedherein. This exemplary stabilizing system 211 includes first and secondconcentric springs 212, 214 as part of stabilizing member 210 that ispositioned between first and second pedicle screws 216, 218, asgenerally shown in the exploded view of FIG. 8. As those skilled in theart will appreciate, the springs that are incorporated in stabilizingmember 210 may take a variety of forms known to those skilled in theart, for example, machine springs, wire coil springs, wave springs, andthe like, without departing from the spirit or scope of present theinvention. In addition, it is contemplated that other resistance devicesmay be incorporated in stabilizing member 210, for example, elastomericmaterials and/or elastomeric structures, Belleville washers, and thelike (such alternative resistance devices being used alone or incombination with the foregoing springs), without departing from thespirit or scope of the present invention.

Stabilizing system 211 generally defines a first end 220 and a secondend 222. The schematic depiction of FIG. 8 includes a pair of pediclescrews (216, 218), but it is to be understood that the “first end”and/or the “second end” may form intermediate locations, with additionalpedicle screw and/or stabilizing members positioned therebeyond. Towardthe first end 220, a first attachment member 224 is provided that isconfigured and dimensioned to receive a first ball (or sphericalelement) 262 a to define a first ball joint 226 that accommodatesrelative movement between the first attachment member 224 and pediclescrew 216. Indeed, the dynamic junction formed at ball joint 226advantageously provides three rotational degrees of freedom. Toward thesecond end 222 of stabilizing system 211, a second attachment member 228is provided that is configured and dimensioned to receive a second ball(or spherical element) 262 b to define a second ball joint 230. Thesecond ball joint advantageously accommodates relative movement betweenthe second attachment member 228 and pedicle screw 218, i.e., defines adynamic junction that provides three rotational degrees of freedom.

In the exemplary embodiment of FIG. 8, ball joints 226, 230 include asocket 232, 234 formed integrally with the respective first and secondattachment members 224, 228 and a ball or sphere 236, 238 positionedtherein. Of course, sockets 232, 234 may be fabricated as separatecomponents from first and second attachment members 224, 228 withoutdeparting from the spirit or scope of the present disclosure. Inimplementations wherein the sockets are fabricated separately from theattachment members, appropriate mechanisms for joining/connection suchsub-assemblies may be employed, e.g., welded connections, threadedengagements, bayonet locking mechanisms or the like.

According to the exemplary embodiment of FIGS. 8-17, the firstattachment member 224 is structured for supporting the inner firstspring 212 for operation in accordance with the present stabilizingsystem 211. As best seen in FIGS. 16 and 28, the first attachment member224 includes a body member 240 having an aperture 242 extendingtherethrough. The inner surface of aperture 242 defines socket 232 andis shaped and dimensioned for receipt of ball (or spherical element)236. The assembly of the ball/spherical element is achieved by rotatingthe ball 90 degrees off of the normal position of the ball relative tosocket 232. At this position the ball/spherical element can slidethrough two opposed slots 232 a cut in the internal spherical race ofthe socket. In exemplary embodiments of the present disclosure, theopposed slots are substantially arcuate and extend for a distance thataccommodates the height of the spherical element. Once positioned withinthe socket, the ball/spherical element is generally rotated relative tothe socket to prevent disengagement therefrom. Indeed, once assembledonto the pedicle screw, there is no possibility of the ball/sphericalelement coming disassembled from the internal spherical race formed inthe socket member. In exemplary embodiments of the present disclosure,aperture 242 is sized such that ball/spherical element 236 engagessocket 232 at or near a plane that defines the diameter ofball/spherical element 236. In this way, ball/spherical element 236 iscentrally positioned relative to socket 232 and is not permitted to passthrough socket 232. The inner first spring 212 extends from, and in anexemplary embodiment is integrally formed with, the body member 240 ofthe first attachment member 224.

The second attachment member 228 similarly includes a body member 244having an aperture 246 extending therethrough. The inner surface of theaperture 246 defines a socket 234 that is shaped and dimensioned forreceipt of the ball 238. Thus, in exemplary embodiments, socket 234includes opposed slots to accommodate introduction of a ball/sphericalelement, as described above with reference to socket 232. As with thedimensional relationship between ball 236 and socket 232, aperture 246is advantageously dimensioned such that ball 238 is engaged by socket232 at or near a plane that defines the diameter of ball 238 (and ball238 is not permitted to pass through socket 232). The second attachmentmember 228 further includes a rod connector 248 with a transverseaperture or channel 250 extending therethrough. The transverse apertureor channel 250 is shaped and dimensioned for passage of spring cap rod252 therethrough. The spring cap rod 252 is secured within thetransverse aperture 250, e.g., via a set screw 254 extending through athreaded aperture that provides a channel from the external surface ofthe rod connector 248 and the transverse aperture/channel 250 withinwhich is positioned spring cap rod 252.

In accordance with an alternate embodiment, and with reference to FIG.10, set screw 254′ interacts with a wedge member 249′. The wedge member249′ is seated within transverse aperture/channel 250′ and is shaped anddimensioned for engaging the spring cap rod 252 as it passes through thetransverse aperture/channel 250′. More particularly, the wedge member249′ includes an exposed arcuate surface that is shaped and dimensionedto interact with spring cap rod 252′ to substantially prevent movementof the spring cap rod relative to the second attachment member 228′ whenset screw 254′ is tightened against wedge member 249′.

With reference to FIGS. 11, 15 a and 15 b, a further alternativestructural arrangement for securing a spring cap rod relative to anattachment member according to the present disclosure is schematicallydepicted. The structural arrangement of FIGS. 11, 15 a and 15 b may beparticularly advantageous when it is desirable to provide flexibleloading of the spring cap rod within the attachment member. Thealternate embodiment of FIGS. 11, 15 a and 15 b employs a selectivelyrotatable ball 249″ within transverse aperture/channel 250″ defined inattachment member 228″. The ball 249″ includes a transverse compressionslot 251″ extending therethrough. A plurality of internal grooves 253opening into opening 255 are also formed in ball 249″ to furtherfacilitate gripping of a spring cap rod 252″ positioned therewithin, asdescribed in greater detail below. Of note, opening 255 formed in ball249″ and shown in FIG. 15 b is advantageously elliptical in geometry,with a minor axis “Y” and a major axis “Z”. Compression slot 251″ issubstantially aligned with the minor axis “Y” and grooves 253 aredeployed in an arcuate manner in facing relation to compression slot251″, i.e., on the opposite side of opening 255.

In use, after an element is positioned within opening 255, e.g., anelongated member such as a rod, a mechanism (e.g., set screw 254″) isused to apply a force to the exterior of ball 249″. The force isadvantageously applied to ball 249″ in substantial alignment with themajor axis “Z” of elliptical opening 255. As force is applied to theouter surface of ball 249″, the elliptical opening 255 is deformed andassumes a circular (or substantially circular) geometry. Deformationinto a circular geometry is facilitated by the positioning ofcompression slot 251″ and grooves 253 relative to opening 255. Indeed,the positioning of compression slot 251″ and grooves 253 accommodatespreferential deformation of ball 249″ to a desired circular (orsubstantially circular) opening 255. By assuming acircular/substantially circular geometry, the inner wall of ball 249″around opening 255 engages an elongated member/rod of circular crosssection around substantially the entire circumference of the elongatedmember/rod. By engaging the elongated member/rod around substantiallythe entire circumference thereof, greater security is imparted betweenthe ball and the elongated member/rod.

Thus, the slot 251″ and grooves 253 allow the ball 249″ to be compressedand deformed to a limited degree by force imparted by the set screw254″, thereby locking the ball 249″ and spring cap rod 252″ in positionwithin the transverse aperture/channel 250″. The ball 249″ allows thespring cap rod 252″ to extend therethrough while the orientation of theball 249″ and spring cap rod 252″ relative to the second attachmentmember 228″ is adjusted to a desired orientation. Stated differently,ball 249″ has three degrees of rotational freedom withinaperture/channel 250″ such that the ball 249″ can be oriented atessentially any angle to accommodate alignment with spring cap rod 252″(or another elongated member/rod), thereby greatly enhancing the easeand flexibility of assembly associated with a spinal stabilizationsystem. Indeed, a rod positioned within ball 249″ is generallytrimmed-to-length by a clinician/surgeon once assembled with anattachment member; if trimmed very close to the exiting edge of ball249″, the ball/rod combination will exhibit essentially 180° ofrotational freedom relative to attachment member 228″. Highdegrees/levels of angulation, as are accommodated by the exemplaryembodiments disclosed herein, are generally advantageous in clinicalapplications. The combination of ball 249″ with aperture/channel 250″ ofattachment member 228″ may be termed a “ball-in-a-box.” Once the desiredorientation is achieved for the rod relative to other components of aspinal stabilization system, the set screw 254″ may be tightened and theassembly is thereby locked in position.

With further reference to FIG. 8, the first and second attachmentmembers 224, 228 are adapted to be mounted upon pedicle screws 216, 218.Each of the pedicle screws 216, 218 includes a proximal end 256 and adistal end 258 (inasmuch as the first and second pedicle screws 216, 218in the exemplary embodiment depicted herein are identical, the samenumeric designations will be used in describing both pedicle screws;however, it is contemplated that pedicle screws having differingstructural and/or functional features may be incorporated intostabilizing system implementations according to the present disclosurewithout departing from the spirit or scope hereof). The distal end 258includes traditional threading adapted for secure attachment along thespinal column of an individual. According to exemplary embodiments ofthe present disclosure and with further reference to FIG. 23, theproximal end 256 of pedicle screw 216 is provided with a collet 260 thatis sized for receipt in a substantially cylindrical receivingaperture/channel 262 a formed within ball/spherical element 236.

Collet 260 is fabricated and/or formed with an ability to expand andcontract, e.g., under the control of medical practitioner(s) involved inusing stabilizing system 211. Exemplary collet 260 includes a pluralityof upstanding segments 264 that are arranged in a substantially arcuatemanner around a central cavity 266, i.e., around the periphery ofcentral cavity 266. Adjacent upstanding segments 264 are separated by aslot or channel 265. As shown in FIG. 23, slot 265 may define anenlarged, substantially circular region 265 a at a base thereof. Inexemplary embodiments of the present disclosure, circular region 265 afurther facilitates relative movement of adjacent upstanding segments264.

With further reference to FIGS. 8 and 23, exemplary collet 260 definesthree (3) upstanding segments 264 that are substantially identical ingeometry/dimension, although alternative numbers, spacings and/orarrangements of upstanding segments 264 may be utilized and/or employedwithout departing from the spirit or scope of the present disclosure. Aswill be explained below in greater detail, the upstanding segments 264are adapted for movement between: (i) an expanded (or outwardlydeflected) state for locking collet 260 within a receiving channel 262a, 262 b of a ball/spherical element 236, 238 and (ii) an unexpanded (orrest) state wherein the collet 260 may be selectively inserted orremoved from a receiving channel 262 a, 262 b of a ball/sphericalelement 236, 238. Of note, the “expanded state” is generally notassociated with a fixed or predetermined degree of expansion, but ratheris generally defined by the level of expansion (i.e., outwarddeflection) required to achieve a desired frictional engagement betweencollet 260 and ball/spherical element 236, 238.

According to exemplary embodiments of the present disclosure, each ofthe receiving channels 262 a, 262 b of the respective balls/sphericalelements 236, 238 is configured and dimensioned for receiving a collet260 associated with a pedicle screw 216, 218 while in its unexpanded (orsubstantially unexpanded) state. Retention of the collet 260 may befurther enhanced by the provision of a lip 268 at (or adjacent) thedistal or upper end of upstanding segments 264 of collet 260. A lip 268is generally formed on each upstanding segment 264, e.g., during themolding or machining of collet 260, and generally extends around theavailable perimeter of collet 260. Each of the receiving channels 262 a,262 b generally includes first and second chamfered regions at oppositeends thereof. The chamfered regions facilitate alignment and connectionof components of the disclosed stabilizing system, e.g., interactionbetween pedicle screws 216, 218 and balls/spherical elements 236, 238.To facilitate flexibility in use of the disclosed stabilizing system,balls/spherical elements 236, 238 are generally symmetric around orrelative to a mid-plane (designated by phantom line “MP” in FIG. 23).Accordingly, the chamfered regions at either end of receiving channels262 a, 262 b are substantially identical in geometry and dimension.

As noted above, lips 268 are formed on the outer walls of upstandingsegments 264 and are advantageously configured and dimensioned tocooperate with the chamfered regions of receiving channels 262 a, 262 b.Thus, once collet 260 is extended through a receiving channel 262 a, 262b, the lips 268 associated with upstanding segments 264 are generallypositioned in a chamfered region associated with the receiving channel262 a, 262 b. Frictional interaction between the lips 268 and thechamfered face of the receiving channel 262 a, 262 b generally helps tomaintain relative positioning of the collet 260 and the receivingchannel 262 a, 262 b, e.g., both before and after expansion of thecollet 260 as described herein.

According to exemplary embodiments of the present disclosure, structuralfeatures and/or elements are provided on ball/spherical element 236, 238and/or collet 260 to facilitate interaction with one or more tools,e.g., tools for securing a ball/spherical element 236, 238 relative to apedicle screw 216, 218 and/or other components associated withstabilizing system 211. With reference to the exemplary system of FIGS.8 and 23, alignment tabs or cut-outs 270, 272 are fowled in upstandingsegments 264 for tool interaction. The alignment tabs/cut-outs 270, 272shown in FIG. 23 have a substantially L-shaped geometry, althoughalternative geometries may be employed to accommodate specific tooldesigns and/or tool interactions. In the exemplary embodiment of FIGS. 8and 23, a tool (not pictured) may advantageously interact with adjacentalignment tabs/cut-outs 270, 272, e.g., through arcuately arrangedgripping extensions that are spaced, configured and dimensioned toengage/cooperate with adjacent alignment tabs/cut-outs. As noted above,balls/spherical elements 236, 238 are generally symmetric relative to amid-plane (“MP”) and the disclosed alignment tabs/cut-outs 270, 272 aretypically formed at both ends of balls/spherical elements 236, 238.Indeed, the provision of alignment tabs/cut-outs 270, 272 on both endsof balls/spherical elements 236, 238 advantageously facilitates themounting of a ball 236, 238 in either orientation without sacrificingfunctionality/interactivity, e.g., interaction with an ancillary tool orthe like. According to exemplary embodiments of the present disclosure,complementary notches 271 may be formed in balls 236, 238 to facilitatetool interaction. Notches 271 are generally spaced around the peripheryof ball 262 a, 262 b, and may be brought into alignment with cut-outs270, 272, e.g., by rotational reorientation of ball 262 a, 262 brelative to collet 260, by a tool (not shown) in connection withtool-related manipulation thereof. Also, there can be geometry and/orstructure on the pedicle screw which is configured to interact with thecut-outs on the ball/spherical element to automatically orient andprovide rotational stability to allow for counter torque, e.g., whenfixing the ball/spherical element relative to the pedicle screw.

Expansion of the exemplary collet 260 associated with pedicle screw 216,218 may be achieved by the insertion of a set screw 274 within thecentral aperture 266 defined within upstanding segments 264 of collet260. In accordance with an exemplary embodiment, set screw 274 issecured within the central aperture 266 via mating threads formed alongthe inner surface of the central aperture 266 and the outer surface ofthe set screw 274. Set screw 274 generally includes an outwardly taperedportion 274 a, e.g., at or adjacent the non-threaded end thereof, whichis configured and dimensioned to engage upstanding segments 264 ofcollet 260 as screw 274 is threaded relative to pedicle screw 216, 218.Thus, as set screw 274 moves downwardly within the central aperture 266,the upstanding segments 264 are contacted by the outwardly taperedportion 274 a of screw 274 and are forced/deflected outwardly. Outwarddeflection of upstanding segments 264 increases the effective diameterof the collet 260, increasing (or establishing) interference contactbetween the outer surface of collet 260 and the inner wall of receivingchannel 262 a, 262 b. By further insertion of set screw 274, collet 260may be brought into locking engagement with the receiving channel 262 a,262 b of ball/spherical element 236, 238. As noted previously, lips 268may be provided on the outer surface of upstanding segments 264 to,inter alia, enhance the “locking” forces imparted by collet 260.

With reference to FIGS. 24 a, 24 b and 24 c, an alternative collet-basedsystem for securing or mounting a ball/spherical element relative to apedicle screw according to the present disclosure is depicted. Thecollet-based system of FIGS. 24 a-24 c is similar to the system depictedin FIG. 23. However, in the system of FIGS. 24 a-24 c, an internal snapring 273 is provided that is configured to cooperate with an externalring groove 277 formed in the outer wall of upstanding segments 264 andan internal ring groove 279 formed in ball/sphere 236. Snap ring 273defines a partial circle, with opening 273 a facilitating expansion ofthe diameter of snap ring 273. Typically, snap ring 273 is fabricatedfrom an appropriate metallic material, e.g., titanium or stainlesssteel, that provides a desired degree of elasticity. The depths ofexternal and internal ring grooves 277, 279, respectively, are generallyselected to ensure seating of snap ring 273.

In use, snap ring 273 is typically positioned in the internal grooveformed in the ball/spherical element and essentially “snaps” into placewith the outer groove formed in the collet, i.e., when the componentsreach the desired alignment. This “snap” connection between theball/spherical element and the collet/pedicle screw allows the clinicianto take appropriate steps to more permanently secure the componentsrelative to each other (e.g., locate and position appropriate tools)without risk that the components will become misaligned. Thus, the snapring advantageously aligns with and partially nests within both ringgrooves 277, 279, thereby providing a further engagement betweenball/sphere 236. As set screw 274 is screwed into place, the upstandingsegments 264 deflect outward, thereby providing a greater engagementbetween ball/sphere 236 and pedicle screw 216. In alternative embodimenthereof, the snap ring may be initially positioned on the outer surfaceof the collet (i.e., in the outer groove), in which case the snap ring“snaps” into the inner groove of the ball/spherical alignment when thedesired alignment is achieved.

Of note, with a snap ring included in the disclosed assembly, the colletis no longer required to deform both inwardly and outwardly. Thefunction of the lip on the collet may be replaced by the snap ring whichseparates the function of the temporary snap fit and final securement.Due to this separation of mechanical function imparted by snap ring 273,the depth of slots/channels 265 may be reduced in the exemplaryembodiment of FIGS. 24 a-24 c relative to the embodiment of FIG. 23,without diminishing the effectiveness of secure interaction between theball/spherical element and the collet. The potential for reducing thedepth of slots/channels 265 arises because the slots/channels no longerneed to allow deformation inward. Since only outward deflection ofupstanding segments 264 is required to achieve the requisite securingforce, the slot/channel depth may be reduced, thereby stiffening andstrengthening the collet. The selection of an appropriate depth forslots/channels 265 is well within the skill of persons skilled in theart based on the present disclosure. By reducing the depth ofslots/channels 265, greater strength may be imparted to collet 260.

With reference to FIGS. 25 a-25 c, a further alternative mechanism isdepicted wherein the collet is non-deflecting, i.e., the slots/channelsfrom the preceding embodiments are eliminated. Thus, collet 260′ definesa substantially cylindrical structure, rather than a plurality ofupstanding, deflectable segments that are separated by slots/channels265, as described with reference to the preceding embodiments. Thecylindrical structure imparts additional strength to collet 260′,relative to the previously described slotted embodiments. As with theembodiment of FIGS. 24 a-24 c, an internal snap ring 273 is provided andis adapted to nest within internal and external ring grooves 277, 279 inthe manner described above. interaction between snap ring 273 and ringgrooves 277, 279 provides a securing force between collet 260′ andball/sphere 236.

With particular reference to the exploded view of FIG. 25 b and thecross-sectional view of FIG. 25 c, set screw 274′ defines an enlargedhead 274 a that is dimensioned to cooperate with the chamfered openingto ball/sphere 236. A tapered, circumferential bearing surface 274 b isdefined on the lower portion of head 274 a, which is adapted to engageball/sphere 236 as set screw 274′ is screwed into collet 260′.Cooperating screw threads are generally defined on the exterior of thedownwardly extending portion of set screw 274′ (e.g., 6-32 thread) andon the inner surface of collet 260′. Thus, as set screw 274′ is advancedinto collet 260′, bearing surface 274 b engages a cooperating chamferedsurface on ball/sphere 236. At the same time, an angled, circumferentialbearing surface 261 that is defined by (or associated with) pediclescrew 216 is brought into engagement with the symmetrically defined,chamfered surface at the opposite end of ball/sphere 236. Thus, theball/sphere 236 is effectively captured between the enlarged head of setscrew 274′ and bearing surface 261 is positioned adjacent the base ofcollet 260′.

According to the alternative embodiment of FIGS. 25 a-25 c, the strengthof the collet is increased through elimination of the slots/channels. Inaddition, the greater size of the enlarged head of set screw 274′permits a larger hexagonal (or other geometrically shaped) toolengagement feature relative to the previously described embodiments.Moreover, a “tissue-friendly” surface feature 274 c may be defined onthe upper surface of the enlarged head to shield tissue from the spacewithin ball/spherical element 236. However, according to the embodimentof FIGS. 25 a-25 c, it is not possible to “preload” set screw 274′within the central aperture formed within pedicle screw (as described ingreater detail below) because it is not possible to pass theball/spherical element thereover.

With reference to FIGS. 26 a-26 c, a further exemplary mechanism forsecuring or mounting a ball/sphere relative to a pedicle screw isdepicted according to the present disclosure. As with the embodiment ofFIGS. 25 a-25 c, a non-slotted collet is provided in association withpedicle screw. Also, as with the preceding embodiment, an angled,circumferential bearing surface 261 is positioned adjacent the base ofthe collet and is configured and dimensioned to engage an inner surfacedefined by the ball/sphere. Bearing surface 261 is defined by (orassociated with) pedicle screw 216 and is positioned below the screwthreads discussed below.

With particular reference to FIGS. 26 b and 26 c, ball/spherical element236′ defines a threaded inner surface 236 a that is adapted to cooperatewith an outwardly threaded surface 260 a formed on collet 260″. Thecooperating threads obviate the need for, and utility of, the snap ringsdiscussed with reference to prior embodiments. Of note, one or morefeatures are generally formed at the openings of ball/sphere 236′ tofacilitate interaction with a tool (not pictured) for impartingrotational motion of ball/sphere 236′ relative to pedicle screw 216. Inlike measure, one or more features are generally formed at (or near) thetop of collet 260″ to facilitate interaction with a counter-torque tool(not pictured) to ensure that rotation of ball/sphere 236 results in thedesired tightening of ball/sphere 236′ relative to collet 260″. Ashall/sphere 236′ is tightened relative to collet 260″, the bottomportion of the ball/sphere engages bearing surface 261, therebyproviding further frictional engagement therebetween.

In use, the mounting mechanism of FIGS. 26 a-26 c obviates the need fora set screw (as described in previous embodiments) and utilizes anon-slotted collet, thereby imparting additional strength to the colletstructure relative to previously disclosed slotted collets. Assembly ofthe ball/sphere and the pedicle screw requires thread alignment andappropriate tool interaction to effect the desired rotation of theball/sphere relative to the collet/pedicle screw.

With reference to FIG. 27, a further alternative mounting mechanism isdepicted wherein entry threads 236 b on the ball/sphere 236″ areconfigured to interact with cooperative threads 260 x at (or near) thebase of slotted collet 260 k. A snap ring 273 is provided to supplyfurther mounting security as the upstanding segments of the slottedcollet 260 k are deflected outward, i.e., when set screw 274 is advanceddownward relative to pedicle screw 216. According to exemplaryembodiments of the disclosed mechanism, the entry threads are“left-handed” threads, thereby minimizing the potential fordisengagement thereof as set screw 274 is introduced. Indeed, as the setscrew is advanced, the ball/sphere is urged into a locked position dueto the oppositely oriented threading thereof. Alternatively, the setscrew could be provided with left-handed threads, and the entry threadscould be right-handed to achieve the same result. In use, the mountingmechanism of FIG. 27 provides enhanced mounting security between theball/sphere and the collet/pedicle screw through the combinedcontributions of the deflectable upstanding segments of the collet (inresponse to set screw introduction), the inclusion of the snap ring, andthe inclusion of entry threads on the ball/sphere.

According to exemplary embodiments of the present disclosure, set screw274 is advantageously “preloaded” within central aperture 266, i.e., setscrew 274 is partially threaded into central aperture 266 prior tocommencing the clinical procedure. For purposes of the mountingmechanisms described above, only the design of FIGS. 25 a-25 c is notsusceptible to a “preloaded” set screw (because of the enlarged head onset screw 274′). An interference may be provided on the surface of setscrew 274 to maintain the set screw 274 in an initial “preloaded”position, e.g., during shipment and initial clinicalpositioning/introduction of the pedicle screw relative to a patient. Anexemplary interference according to the present disclosure involves adeformation in the helical thread, e.g., at or near a distal endthereof. The deformation may be effected by striking the formed threadin one or more locations (e.g., two opposed locations) with a rigidsurface. In an exemplary embodiment, a pair of deformations or “pings”are formed in the screw thread at or near the distal end of the setscrew. It is further contemplated that a desired interference may beachieved by providing a limited region of “off-pitch” threading alongthe length of the screw thread. Alternative structures and/or mechanismsmay be employed to achieve the desired interference (which is easilyovercome by the clinician when he/she advances the set screw relative tothe pedicle screw), as will be readily apparent to persons skilled inthe art from the present disclosure.

By “preloading” the set screw as described herein, clinical use of thedisclosed system is facilitated, e.g., potential difficulties associatedwith aligning set screw 274 with central aperture 266 during a clinicalprocedure and/or the potential for misplacing/dropping and/orcross-threading the set screw in connection with clinical activities aresubstantially eliminated. Of note, the length of set screw 274 and/orthe relative dimensions and/or positioning of the outwardly taperedregion of set screw 274 may be advantageously selected so as prevent orlimit outward deflection of upstanding segments 264 in the “preloaded”configuration of set screw 274.

In general, tightening and/or locking of a ball/spherical elementrelative to a pedicle screw is thus undertaken according to exemplaryembodiments of the present disclosure by threading a set screw into acentral aperture positioned at or near the head of the pedicle screw.The set screw may be advantageously pre-loaded into the central apertureto facilitate clinical use thereof. Threading of the set screw into thecentral aperture causes an outward deflection of a series of upstandingsegments associated with a collet mechanism associated with the pediclescrew. To facilitate movement of the set screw relative to the pediclescrew, it is generally desirable to impart a “counter-torque” force tothe pedicle screw so as to prevent/limit rotational motion of thepedicle screw as the set screw is inserted or withdrawn relative to thecentral aperture. Tools for providing a desired counter-torque (and forinserting/withdrawing a set screw) are known. According to exemplaryembodiments of the present disclosure, cut-outs/alignment tabs may beformed or associated with the collet and cooperative notches may beformed or associated with the ball/spherical element to facilitateinteraction with such tools, e.g., a tool for imparting a desiredcounter-torque force to the pedicle screw during set screwinsertion/withdrawal.

Although the present disclosure has described a series of exemplaryembodiments wherein a ball/spherical element is mounted with respect toa pedicle screw and cooperates with a socket member to support motionrelative to the pedicle screw (i.e., act as a motion interface element)and provide an advantageous dynamic junction, it is to be understoodthat the present disclosure is not limited to dynamic junctions formedthrough interaction between a ball/spherical element and a socketmember. For example, as shown in FIG. 29, a pedicle screw 216 having anoutwardly threaded collet 260 a may engage an inwardly threaded cavity236 a that is mounted or jointed to a first universal joint mechanism241 which functions as a motion interface element. A rod 252 cooperateswith first universal joint mechanism 241 at a first end thereof and asecond universal joint mechanism 243 at an opposite end thereof. Thedesign and operation of universal joint mechanisms are well known topersons skilled in the art and implementation thereof in connection withpedicle screw mounting structures of the type disclosed herein provideadvantageous alternative dynamic junctions for use in stabilizationsystems/applications. Alternative dynamic junction assemblies may alsobe employed without departing from the spirit or scope of the presentdisclosure, as will be readily apparent to persons skilled in the artfrom the detailed description provided herein.

As those skilled in the art will certainly appreciate, efficient andreliable alignment of ball/spherical element 236, 238 relative to collet260 and within socket 232, 234 is desirable. In accordance withexemplary embodiments of the present disclosure and with reference toFIGS. 12 and 14, alignment activities are facilitated by providingclinicians with an advantageous guidewire system 275. Exemplaryguidewire system 275 includes a guidewire 276 and a tapered guide member278 that defines an outwardly tapered guiding surface (e.g., a conicalsurface) that is shaped and dimensioned to facilitate positioning of aball relative to a pedicle screw and/or socket systems, as describedherein. Guidewire 276 generally defines a proximal end 280 and a distalend 282 with a central portion 284 therebetween. In exemplaryembodiments of the present disclosure, the proximal and distal ends 280,282 of guidewire 276 are substantially similar to conventionalguidewires that are used in conventional pedicle screw installations.However, the central section 284 is provided with an advantageoustapered guide member 278, as described herein.

Tapered guide 278 generally defines a sloped, outer surface and a base279 that is substantially planar. Base 279 is generally dimensioned tohave a maximum diameter that is slightly smaller than that of thediameter of receiving channel 262 a, 262 b (as measured in thenon-chamfered regions). Typically, the difference in diameter betweenbase 279 of tapered guide 278 and the central channel of receivingchannel 262 a, 262 b is about 0.001″ to about 0.020″, therebyfacilitating alignment of a ball relative to a pedicle screw whilesimultaneously ensuring non-obstructed passage of the ball relative tothe base of the tapered guide. In exemplary embodiments of the presentdisclosure, the distal end 282 of guidewire 276 extends within thepedicle screw 216, 218, .g., to a position short of the distal end 258of the pedicle screw 216, 218. The tapered guide member 278 is thenadvantageously positioned on guidewire 276 such that base 279 isadjacent the proximal end 256 of the pedicle screw, e.g., adjacent or incontact with collet 260.

In use, a pedicle screw may be introduced into a desired anatomicallocation. The disclosed guidewire system may, then be advantageouslyemployed to facilitate efficient and reliable positioning of aball/sphere relative to the pedicle screw. The guidewire is generallyfed into the pedicle screw such that the base of the disclosed taperedguide member is brought into close proximity and/or contact with theproximal end of the pedicle screw, e.g., the collet positioned at ornear the head thereof. In percutaneous applications, however, theguidewire is generally positioned first, with the pedicle screwintroduced to a desired anatomical location over the guidewire. Aball/spherical element (or alternative accessory structure) is then fedalong the guidewire, i.e., the guidewire passes through the receivingchannel of a ball/spherical element. The tapered guide memberadvantageously guides the ball into alignment with the proximal end ofthe pedicle screw, e.g., into alignment with a collet positioned at thehead of the pedicle screw. The ball/sphere then passes over the base ofthe tapered guide member into position at the head of the pedicle screw,e.g., with an advantageous collet of the present disclosure positionedwithin the receiving channel of the ball.

It is contemplated that the tapered guide member of the presentdisclosure may be formed with various shapes designed to suit specificneeds and/or applications. For example, the tapered guide member may bespirally shaped and provided with additional guides for ensuring that aball has a proper orientation/registration when seated upon the collet.Such an embodiment might be used in minimally invasive procedures, e.g.,to facilitate proper alignment with a set screw of an attachment member.In addition, the tapered guide member may advantageously includestructures and/or features to facilitate rotational alignment orregistration of a component, e.g., a component having at least oneasymmetrical characteristic, relative to a pedicle screw. Thus, forexample, a spiral may be provided on the tapered guide member thatensures proper alignment/registration with feature(s) on the pediclescrew.

In addition, a guiding cone or tapered guide member may be usedaccording to the present disclosure to guide a screwdriver and/or acounter-torque device down the guidewire, e.g., to facilitate accessingof the set screw with limited or non-existent visualization. In anadditional advantageous embodiment of the present disclosure, theguidewire system may facilitate tool alignment/guidance to an off-axislocation, e.g., a laterally spaced attachment member and/or rodconnector, based on a known lateral/off-axis direction and distancerelative to the pedicle screw in which the guidewire is positioned.Thus, a guide member may be slid along the guidewire that effects apredetermined and advantageous off-axis positioning of, for example, atool (e.g., a screw driver) relative to the guidewire.

Further, a tapered guide member according to the present disclosure mayhave a star-shaped or triangular profile. In addition, the tapered guidemember may be provided as a separate component, i.e., for assembly withthe guidewire at a desired point in time, e.g., during installation of astabilization system according to the present disclosure. Inimplementations where the tapered guide member is provided as a distinctcomponent relative to the guidewire (as opposed to a pre-assembledguidewire system), the tapered guide member is advantageously passedover the guidewire and positioned at a desired axial position during thestabilization system installation process. Indeed, it is furthercontemplated that the tapered guide member may be formed and usedseparately from a guidewire, e.g., by placing the tapered guide memberin juxtaposition with the proximal end of a pedicle screw, e.g., bymounting a tapered guide member relative to a collet that is associatedwith a pedicle screw.

With further reference to the biasing structures of exemplarystabilizing member 210, a piston assembly 286 is provided that includesconcentric springs 212, 214. The concentric springs take the form of aninner first spring 212 and an outer second spring 214. As will bedescribed below in greater detail, the piston assembly 286 furtherincludes a spring cap 288 and a spring cap rod 252 which translateand/or transmit forces between piston assembly 286 and pedicle screws216, 218. Inasmuch as pedicle screws 216, 218 are substantially integralwith spinal structures of a patient, the structural arrangementdescribed herein effectively translates and/or transmits forces to andfrom a patient's spine.

The inner first spring 212 generally defines a first end 290 and asecond end 292. As mentioned above, in exemplary embodiments of thepresent disclosure, first spring 212 is rigidly secured to firstattachment member 224. The second end 292 of the inner first spring 212is rigidly secured to abutment surface 294 of spring cap rod 252. Theouter second spring 214 also defines a first end 296 and a second end298. In exemplary embodiments of the present disclosure, the first end296 of the outer second spring 214 is rigidly secured to spring cap 288and the second end 298 of outer second spring 214 is rigidly secured toabutment surface 294 of spring cap rod 252.

As discussed above, the respective first and second springs 212, 214 arecoupled to one or more structures associated with the exemplarystabilizing member 210. According to exemplary embodiments hereof, oneor both springs 212, 214 may be rigidly (i.e., fixedly) coupled withrespect to one or more component(s) associated with stabilizing member210. In accordance with a preferred embodiment of the presentdisclosure, the springs are welded to structures at one or both endsthereof, although those skilled in the art will appreciate that othercoupling techniques (e.g., nesting and/or capturing techniques) may beused without departing from the spirit or scope of the presentinvention.

The springs 212, 214 are generally positioned within a sheath 300, e.g.,a substantially cylindrical member, to prevent undesirable interactionor interference between the springs and anatomical structures in situ.Thus, sheath member 300 is advantageously substantially inert withrespect to surrounding anatomical structures and fluids. In accordancewith exemplary embodiments of the present disclosure, sheath 300 isfabricated (at least in part) of ePTFE (expandedpolytetrafluoroethylene), UHMWPE (Ultra-High Molecular WeightPolyethylene), polycarbonate-urethane composite materials (e.g.,copolymers and/or blends thereof), or combinations thereof, althoughthose skilled in the art will appreciate that other materials may beused without departing from the spirit or scope of the presentinvention. Sheath 300 is generally fabricated from a material withsufficient elasticity to accommodate axial elongation/contraction ofstabilizing member 110, although structural arrangements to accommodatesuch axial motion, e.g., a bellows-like structure, may also be employed.It is contemplated that sheath 300 may include a surface treatment,e.g., a drug and/or medicinal agent, to facilitate or promote desiredclinical results.

Abutment surface 294 of spring cap rod 252 is generally secured withrespect to sheath 300 at a first end thereof, and spring cap 288 isgenerally secured with respect to sheath 300 at an opposite end thereof.Washers or C-clamps 302 are generally positioned at the junction betweensheath 300 and the end member (i.e., spring cap 288 and abutment surface294) to facilitate interaction therebetween. In an exemplary embodimentof the present disclosure, spring cap 288 is further rigidly securedwith respect to body member 240 of first attachment member 224.

As shown in FIGS. 8 and 9, first and second springs 212, 214, spring cap288 and spring cap rod 252 generally couple piston assembly 286 topedicle screws 216, 218 in a manner providing a desirable andadvantageous force profile, despite the limited anatomical spaceavailable in spine applications. For example, when the spine moves inextension, pedicle screws 216, 218 encounter forces that bias thepedicle screws toward each other. The forces experienced by pediclescrews 216, 218 are translated to forces on first and second attachmentmembers 224, 228, which similarly are biased to move toward each other.The foregoing forces (that originate from spinal activity) generate acompressive force on stabilizing member 210. In response to thecompressive force experienced by stabilizing member 210, a counterforceis generated within stabilizing member 210 through the spring forcegenerated as spring cap rod 252 pushes and compresses outer secondspring 214 between spring cap 288 and abutment surface 294 of spring caprod 252. An additional counterforce is generated by stabilizing member210 as spring cap rod 252 pushes and compresses the inner first spring212 between the body 240 of the first attachment member 224 and theabutment surface 294 of the spring cap rod 252. As shown in FIG. 17, thecombined spring forces of first spring 212 and second spring 214 createsa substantially uniform force profile in response to spine movement intension, while extension generates compression across the springmember(s).

When the spine moves in flexion, pedicle screws 216, 218 are subject toforces that bias the pedicle screws away from each other. The forcesexperienced by pedicle screws 216, 218 as the spine moves in flexion aretranslated to first and second attachment members 224, 228, whichsimilarly experience a force that biases such components of stabilizingsystem 211 away from each other. A counterforce is generated bystabilizing member 210 in response to flexion motion of the spine. Thecounterforce is generated in part as a result of the spring forcegenerated when the spring cap rod 252 pulls upon and extends outersecond spring 214 between the spring cap 288 and abutment surface 294 ofspring cap rod 252. An additional counterforce is generated in responseto flexion movement of the spine as spring cap rod 252 allows extensionof the inner first spring 212 between the body 240 of first attachmentmember 224 and abutment surface 294 of spring cap rod 252. As the forceprofile of FIG. 17 shows, the operation of springs 212, 214 withinstabilizing member 210 creates a force profile that advantageouslydecreases in intensity as overall spinal displacementincreases/continues. At a certain point the inner spring reaches itsfree length and the resistance to motion is only in response to theincreased elongation of the outer spring.

Referring to FIGS. 8 and 13-16, and in accordance with an exemplaryembodiment of the present disclosure, stabilizer system 211 is generallyinstalled in the following manner. Pedicle screws 216, 218 arepositioned within the vertebrae using traditional techniques. The use offluoroscopy for guidance of the pedicle screws is generally employed andstrongly recommended. The pedicle screws 216, 218 are typically placedlateral to the facets in order to ensure that there is no interferencebetween a facet and the implanted system. The pedicle is first openedwith a high-speed burr or an awl. Thereafter, a stabilizer pedicle probemay be used to create a channel for pedicle screws 216, 218. Thepedicles screws 216, 218 are generally self-tapping and thereforetapping of the pedicle screw channel typically is not required. Theintegrity of the pedicle channel wall is then typically checked and anappropriately sized pedicle screw 216, 218 is installed by attaching thescrew to a screw driver and introducing the screw lateral to the facets.The pedicle screw 216, 218 is generally advanced until the head of thescrew is in contact with the pedicle. Typically, placement of thepedicle screw 216, 218 as low as possible is very important, especiallyin the L5 and S1 pedicles. The placement of the pedicle screws 216, 218is then generally checked with fluoroscopy, X-ray and/or other surgicalnavigation/viewing technique.

Once the pedicle screws 216, 218 are properly installed, the distancebetween the pedicle screws 216, 218 is generally measured and rod 252 ofstabilizing member 210 may be cut to proper dimension, as appropriate.Alternatively, rods 252 of varying length may be provided to permit aclinician to select a rod of desired length. Still further, means foradjusting the length of a rod 252 may be employed, e.g., a telescopingrod with mechanism(s) for securing the rod at one or more desiredlengths (e.g., detent mechanisms at fixed intervals, set screw systemsfor fixing the telescoping rod members relative to each other, or thelike).

In installation procedures that employ a guidewire system to guidealignment and/or installation of system components, guidewire(s) 276 arepositioned within one or both of the pedicle screws 216, 218. Accordingto exemplary embodiments of the present disclosure, a tapered guidemember 278 is advantageously positioned adjacent the top of collet 260.However, as noted previously, a tapered guide member may be directlyassociated with the pedicle screw and/or collet to facilitate alignmentand/or installation of system components (e.g., in implementations thatdo not employ a guidewire).

An attachment member 224, 228 (which encompasses a ball/sphere 236) maybe slid down along a guidewire 276 until a tapered guide 278 is reached.Once the attachment member 224, 228 reaches the tapered guide 278, amore exact guiding function is imparted to the attachment member.Indeed, tapered guide 278 advantageously functions to guide theball/sphere 236 associated with attachment member 224, 228 intoalignment with collet 260 such that it is positioned/aligned forefficient sliding passage thereover. Thus, tapered guide 278 brings thecenter line of the channel formed in ball/sphere 236 into substantialalignment with the center line of collet 260 so that collet 260 canreadily slide through the ball/sphere 236. Depending on the mountingmechanism associated with interaction between the collet and theball/sphere (see FIGS. 23-27), the aligned components are then mountedwith respect to each other.

Thus, in the exemplary embodiment of FIGS. 8 and 15-16, set screw 274 isadvantageously tightened within collet 260 to effect outward deflectionof the upstanding segments, thereby locking/securing the ball 236, 238in position relative to the collet/pedicle screw. Of note, in theexemplary embodiment of FIGS. 8 and 15-16, set screw 274 may beadvantageously preloaded relative to collet 260, thereby facilitatingthe mounting process as described previously. For alternative mountingmechanisms described herein, appropriate steps may be undertaken tosecure the ball/sphere relative to the collet, e.g., rotational motionof ball 236, 238 relative to the collet. Of note, ball 236, 238 isadapted for freely rotational motion relative to attachment member 224,228, thereby facilitating rotational mounting of the ball, if desired.

At this stage of assembly/installation, a first ball is secured relativeto a first collet/pedicle screw. However, according to the presentdisclosure, a dynamic junction is nonetheless established because theattachment member is free to move, e.g., rotate, relative to the ball.Indeed, a “race” is generally defined therebetween to facilitaterelative movement between the ball and attachment member. As such,realignment and/or reorientation of the attachment member is possible soas to facilitate alignment with an adjacent pedicle screw, i.e., forassembly of a dynamic stabilization level. Of particular note, evenafter mounting of an attachment member relative to an adjacent pediclescrew, the dynamic junction remains operative at the initial pediclescrew described herein, thereby accommodating anatomical shifts that mayarise after installation of the disclosed dynamic stabilization system.

With further reference to FIGS. 15-16, rod 252 is aligned with areceiving portion of rod connector 248 that is associated with secondattachment member 228. As with the first attachment member discussedabove, a dynamic junction is advantageously defined between socket 232and ball/sphere 238 such that alignment between rod connector 248 androd 252 is facilitated. Moreover, the functionality of the dynamicjunction is unaffected by mounting of rod 252 relative to rod connector248, i.e., rotational motion therebetween is not affected when a rod issecured/assembled according to the disclosed dynamic stabilizationsystem. When rod 252 is properly aligned within rod connector 248, setscrew 254 is tightened within transverse aperture 250 to lock rod 252 inposition. The installation procedure is generally repeated on theopposite side of the vertebrae to complete a single level dynamicstabilization. Thus, at this stage in the assembly process, a dynamicstabilization is established for a single level, i.e., the level definedby the location of pedicle screws 216, 218 (and the associatedcounterparts on the opposite side of the vertebrae).

With reference to FIGS. 28 and 30 (and corresponding structures in FIGS.8 and 19), additional structural and assembly details associated with anexemplary embodiment of the disclosed dynamic stabilizing member are nowprovided. As noted above, first attachment member 224 includes springcap 228. As shown in FIG. 28, spring cap 228 includes a helical groove229 on the outer periphery of the flange-like structure of spring cap228. The width and depth of groove 229 are generally sized so as toaccommodate the wire gage of a helical outer spring (e.g., second spring214 of FIG. 8 or second spring 456 of FIG. 19). In addition, a post 231extends from the flange-like structure of spring cap 228. Post 231 isgenerally centrally located on the flange-like structure and extendsaway from socket 232. An annular cavity 233 may be formed around post231. According to exemplary embodiments of the present disclosure andwith reference to FIG. 30, abutment surface 294 of spring cap rod 252includes a helical groove 295 (akin to helical groove 229), post 297(akin to post 231) and annular cavity 299 (233). An elongated member(rod) 301 extends from abutment surface 294 in a direction opposite topost 297. The foregoing structures and features facilitate assembly andoperation of exemplary dynamic stabilizing members according to thepresent disclosure.

More particularly, according to exemplary embodiments of the presentdisclosure, inner first spring 212 is initially positioned within second(outer) spring 214, and is then positioned around or on post 231 and theopposed post 297 that extends from abutment surface 294. According toexemplary assemblies of the present disclosure, inner first spring 212advantageously extends into annular cavity 233 and the opposed cavity299 formed in abutment surface 294. In this way, inner first spring 212is effectively captured between spring cap 288 and spring cap rod 252,and essentially floats relative to the opposing posts 231, 297.Thereafter, second spring 214 is threaded into groove 229 formed inspring cap 288 (or the opposed groove 295 formed in abutment surface294). Ultimately, second spring 214 is typically fixed with respectthereto, e.g., by welding, and may be trimmed so as to be flush relativeto an outer edge of the flange-like structure to which it is mounted.The outer second spring 214 is then extended so as to be threaded ontothe opposing groove, i.e., the groove associated with abutment surface294 or spring cap 288, e.g., by rotating abutment surface 294 or springcap 288 relative to second spring 214, as the case may be. Once threadedinto the opposing groove, the second spring 214 is typically fixed withrespect thereto, e.g., by welding, and may be trimmed to establish aflush edge.

Of note, outer second spring 214 is typically shorter than inner firstspring 212. Thus, as abutment surface 294 and spring cap 288 are broughttoward each other (to permit second spring 214 to be mounted on both),inner first spring 212 is placed in compression. The degree to whichfirst spring 212 is compressed is generally dependent on the differencein length as between springs 212, 214. Thus, the preload compression offirst spring 212 may be controlled and/or adjusted in part throughselection of the relative lengths of springs 212, 214. In addition tothe preload compression of inner spring 212, the mounting of outerspring 214 with respect to both spring cap 288 and abutment surface 294places outer spring 214 in tension. The overall preload of a dynamicstabilizing member according to this exemplary embodiment corresponds tothe equal and opposite forces experienced by springs 212, 214, i.e., theinitial tension of outer spring 214 and the initial compression of innerspring 212.

According to exemplary embodiments of the present disclosure, innerspring 212 reaches its free length (i.e., non-compressed state) at orabout the point at which a patient's movement exceeds the neutral zone.Beyond this point, inner spring 212 is free floating (on the opposedposts) and contributes no resistance to spinal movement. As describedpreviously, the advantageous force profile supplied by the dynamicstabilization system of the present disclosure is achieved throughutilization of inner and outer springs working synergistically. Inparticular, the force profiles for the springs are chosen to produce areduction in the increase of mechanical resistance as the displacementmoves beyond the neutral zone.

As briefly mentioned above, an axial spring configuration may beemployed which generates the Force-Displacement curves shown withreference to FIG. 17, while allowing for a shorter distance between thefirst and second attachment members. As noted above, theForce-displacement curve is not exactly the same as that disclosed withreference to the embodiment of FIGS. 1 to 7. That is, the curve issubstantially uniform during extension of the back and compression ofthe stabilizer, but the curve is substantially similar to that describedwith reference to FIGS. 3 a and 3 b when the back is in flexion and thestabilizer is elongated. The exemplary concentric spring design of thepresent disclosure allows a shorter distance between the first andsecond attachment members, eliminates the overhang on some previousembodiments, but this concentric spring orientation dictates that theextension curve be uniform or straight (i no elbow). This profilecharacteristic results from the fact that both springs are loaded inextension, thus creating the exact same curve when both springs areloaded in the neutral zone, as compared to a situation wherein only onespring is loaded in flexion, i.e., while being elongated once outsidethe central zone of the device.

The advantageous dynamic stabilization systems disclosed herein may alsobe used in the stabilization of multiple level systems. Multiple levelstabilization may be achieved through installation of a pluralitystabilizing members coupled through a plurality of elongated members(e.g., rods) and a plurality of pedicle screws. For example and withreference to FIGS. 18 to 22, a multiple level, dynamic stabilizationsystem 410 is schematically depicted. Multi-level stabilization system410 may employ a variety of different attachment members 412, 414, 416.The different attachment member designs may be selected based onanatomical considerations, e.g., the spinal location for installation,and/or the position within the multi-level system. In other words,certain attachment member designs are better utilized at a first end ora second end, whereas other attachment member designs are suited forintermediate locations. While a specific combination of elements and/orcomponents are disclosed in accordance with the exemplary multi-levelstabilization system of FIGS. 18-22, those skilled in the art willreadily understand from the present disclosure how the variousattachment members and related structures/components may be employed toachieve dynamic stabilization at various spinal locations and/or inalternative deployment schemes.

Exemplary multi-level dynamic stabilization system 410 employs threedistinct attachment members 412, 414, 416 dynamically linked by pistonassemblies 418, 420 in the creation of a two level system. Of course,additional levels may be stabilized by extending the assembly withadditional pedicle screws, collet/ball mounting mechanisms, dynamicstabilizing members, and elongated members/rods. The various attachmentmembers are secured to the vertebrae through interaction with pediclescrews (not shown), as described above. Typically a dynamic junction isadvantageously established between each pedicle screw (throughcooperation with a ball/collet mechanism) and the attachment membermounted with respect thereto. The dynamic junction facilitates alignmentwith adjacent pedicle screw/attachment member subassemblies duringinstallation/assembly of the multi-level dynamic stabilization system,and accommodates limited anatomical shifts/realignmentspost-installation.

With regard to dynamic stabilization between the first attachment member412 and the second attachment member 414, the first attachment member412 is structured for supporting inner first spring 428 and includes abody member 430 having an aperture 432 that extends therethrough. Bodymember 430 defines a socket 434 which is configured and dimensioned forreceipt of ball 436, thereby establishing a first dynamic junction.According to the exemplary embodiment depicted herein, the inner firstspring 428 extends from, and may be integrally formed with (or otherwisepositioned with respect to), body member 430 of the first attachmentmember 412.

The second attachment member 414 similarly includes a body member 438having an aperture 440 that extends therethrough. Body member 438defines socket 442 which is configured and dimensioned for receipt ofball 444, thereby establishing a second dynamic junction. Secondattachment member 414 further includes or defines a rod connector 446with a transverse slot or channel 448 that extends therethrough.Transverse slot/channel 448 is configured and dimensioned to accommodatepositioning and/or passage of stabilizer spring cap rod 450 therewithin.Spring cap rod 450 is generally secured within the transverseslot/channel 448 via a set screw 452 that extends between the externalsurface of rod connector 446 and the transverse slot/channel 448 formedby rod connector 446. As those skilled in the art will certainlyappreciate, the transverse channel/slot may be structured in a varietyof ways (e.g., as discussed above with reference to FIGS. 8-11). Secondattachment member 414 is further associated with an inner first spring454 that extends therefrom for interaction with third attachment member416 (discussed below).

Piston assembly 418, which is positioned between first and secondattachment members 412, 414, generally includes a pair of concentricsprings. An inner first spring 428 and an outer second spring 456 aretypically provided. As with the embodiment described above, inner firstspring 428 and outer second spring 456 are secured with respect to anabutment surface 458 of spring cap rod 450 and body member 430 of firstattachment member 412. Thus, first and second springs 428, 456 supplyforces that act on (or with respect to) first and second attachmentmembers 412, 414 during spinal movement, e.g., during extension andflexion of the spine. As is readily apparent from the discussion herein,the forces exerted on first and second attachment members 412, 414 aretranslated to forces on the associated pedicle screws, therebystabilizing the vertebrae to which the pedicle screws are mounted.

Referring now to the relationship between second attachment member 414and third attachment member 416, it is noted that the structuralfeatures of third attachment member 416 are substantially similar tothose of second attachment member 414. However, in exemplary two-levelstabilization systems disclosed herein, third attachment member 416 doesnot have an inner first spring 454 extending therefrom. Piston assembly420 positioned between second and third attachment members 414, 416 issimilar to the previously described piston assemblies. Generally, pistonassembly 420 includes an inner first spring 454 that extends from secondattachment member 414 and spring cap rod 464 extends from thirdattachment member 416.

As mentioned above, first, second and third attachment members 412, 414,416 may have particular utility at particular anatomical locations. Forexample, it is contemplated that first attachment member 412 could bemost useful at position S1 and below position L5, whereas second andthird attachment members 414, 416 may be advantageously employed at L5and above. Alternative implementations of the foregoing attachmentmembers may be undertaken based on particular clinical needs and/orjudgments.

Of note, single or multi-level dynamic spine stabilizationsystems/implementations according to the present disclosure permit oneor more adjustments to be made (e.g., in situ and/or prior to clinicalinstallation). For example, adjustments as to the magnitude and/ordisplacement-response characteristics of the forces applied by thestabilization system may be implemented, e.g., by substituting springswithin one or more of the stabilizing members and/or adjusting thefirst/second housings, as described with reference to FIG. 8. Theadjustments may be made prior to initiating a clinical procedure, e.g.,based on an evaluation of a particular patient, or after a clinicalprocedure, e.g., based on post-surgical experiences of a patient.

According to further exemplary embodiments of the present disclosure,multi-level spinal stabilizations may be undertaken wherein the same ordiffering stabilization modalities may be employed at each of theindividual levels. Thus, for example, a dynamic stabilizing memberaccording to the present disclosure may be employed at a firststabilization level, a non-dynamic stabilizing member (e.g., a rigidstructure/assembly such as a rigid rod or plate connection) at a secondstabilization level, and a dynamic or non-dynamic stabilizing element ata third stabilization level. The advantageous flexibility andversatility of the disclosed systems/designs for mounting relative to apedicle screw enhance the ability to vary the stabilization modalitiesfrom level-to-level according to the present disclosure. For example,upwardly extending collets disclosed herein readily accommodatecooperative mounting with respect to both dynamic and non-dynamicstabilizing members/elements. Indeed, it is contemplated according tothe present disclosure that decisions as to stabilization modalities maybe made at the time of surgery, e.g., based on clinical observationsand/or limitations. Moreover, it is contemplated that dynamic andnon-dynamic modalities may be interchanged at a point in timepost-surgery. In such applications, a first stabilizing member (whetherdynamic or non-dynamic) may be disengaged from a clinically installedstabilization system, and a second stabilizing member that offers adifferent modality may be installed in its place. Thus, systemsaccording to the present disclosure encompass multi-level stabilizationsthat include at least one level that includes a dynamic stabilizingmember and at least one level that includes a non-dynamic stabilizingelement.

A kit may be advantageously provided that contains the components thatmay be necessary to perform clinical procedures according to the presentdisclosure, i.e., spine stabilization procedures. The kit contents aretypically sterilized, as is known in the art, and may includeappropriate labeling/indicia to facilitate use thereof. Typical kitcontents include: (i) two or more attachment members (wherein one of theattachment members may include an extension member that incorporates astabilizing member), (ii) two or more balls/spheres, and (iii) two ormore pedicle screws. Alternative kits according to the presentdisclosure may include one or more of the following additional items:(iv) a variety or assortment of replacement springs for potential use inthe dynamic stabilizing members of the present disclosure, (v) one ormore tools for use in the dynamic stabilization procedures of thepresent disclosure (e.g., a screw driver, counter-torque device,measurement tools, tools for placement of the pedicle screws, etc.),(vi) one or more guidewires, (vii) one or more tapered guides or cones,and/or (viii) one or more set screws. The enclosures for the foregoingkits are typically configured and dimensioned to accommodate theforegoing components, and are fabricated from materials that accommodatesterilization, as are known in the art. A single kit may be broken intomultiple enclosures, without departing from the spirit or scope of thepresent disclosure.

For exemplary embodiments of the present disclosure wherein springs areutilized in fabricating the disclosed dynamic stabilizing members,spring selection is generally guided by the need or desire to deliver aparticular force profile or force profile curve, as described above.Generally, spring selection is governed by basic physical laws thatpredict the force produced by a particular spring design/material.However, the particularly advantageous dynamic spinal stabilizationachieved according to the present disclosure (as described above andschematically depicted in FIGS. 3 a, 3 b and 17) require a recognitionof the conditions and stimuli to be encountered in a spinal environment.

A first design criterion is the fact that the dynamic stabilizing membermust function both in compression and tension. Second, the higherstiffness (K₁+K₂) provided by a disclosed dynamic stabilizing member inthe central zone is generally achieved through the presence of a springpreload. Both springs are made to work together when the preload ispresent. As the dynamic stabilizing member is either tensioned orcompressed, the responsive force increases in one spring and decreasesin the other. When the decreasing force reaches a zero value, the springcorresponding to this force no longer contributes to the stabilizingfunctionality. An engineering analysis, including the diagrams shown inFIGS. 7 a and 7 b, is presented below. This analysis specificallyrelates to the exemplary embodiment disclosed in FIG. 5, although thoseskilled in the art will appreciate the way in which the analysis applieswith equal force to all embodiments disclosed herein.

-   -   F₀ is the preload within the dynamic stabilizing member,        introduced by shortening the body length of the housing as        discussed above.    -   K₁ and K₂ are stiffness coefficients of the compression springs,        active during tensioning and compression of the dynamic        stabilizing member, respectively.    -   F and D are respectively the force and displacement of the disc        of the dynamic stabilizing member with respect to the body of        the dynamic stabilizing member.    -   The sum of forces must equal zero. Therefore,        F+(F ₀ −D×K ₂)−(F ₀ +D×K ₁)=0, and        F=D×(K ₁ +K ₂)    -   With regard to the central zone (CZ) width (see FIG. 3 a):        -   On Tension side CZ_(T) is:            CZ _(T) =F ₀ /K ₂        -   On Compression side CZc is:            CZ _(c) =F ₀ /K ₁

While the foregoing analysis is useful in understanding the physicalproperties and forces associated with operation of the disclosed dynamicstabilizing member, the present disclosure is not limited to anytheoretical or quantitative characterization of spring design orfunction. Rather, desired force profiles/force profile curves may beachieved through quantitative analysis, empirical study, or combinationsthereof. In addition, as those skilled in the art will certainlyappreciate, the concepts underlying the dynamic stabilization systemsand associated components/assemblies may be applied to other clinicalneeds and/or medical/surgical procedures. As such, the discloseddevices, systems and methods may be utilized beyond spinal treatmentswithout departing from the spirit or scope of the present invention.

Having described exemplary embodiments of the present disclosure, it isspecifically noted that the present invention embodies a series ofadvantageous features and functions having particular utility in spinalstabilization devices/systems and associated methods, including thefollowing:

-   -   Devices, systems and methods that provide a dynamic junction        between at least one pedicle screw and at least one elongated        member (or multiple elongated members), e.g., rod(s), that        engage and/or otherwise cooperate with the pedicle screw. In        exemplary embodiments of the present disclosure, the dynamic        junction is provided through interaction between a collet/ball        mechanism and a socket that is associated with an attachment        member. The dynamic junction facilitates assembly of a spinal        stabilization system and permits the pedicle screw/elongated        member to accommodate limited degrees of anatomical        realignment/reorientation post-installation.    -   Devices, systems and methods that provide or incorporate ball        assembly mechanisms that facilitate assembly/installation of a        ball/sphere relative to a pedicle screw and provide advantageous        functional attributes as part of a spinal stabilization system.        Exemplary mechanisms include advantageous collet-based        mechanisms (e.g., slotted and non-slotted collets),        cooperatively threaded mechanisms (e.g., an externally threaded        collet cooperating with an internally threaded ball/sphere),        mechanisms that apply bearing forces against the ball/sphere        (e.g., a circumferential bearing surface formed on a set screw        having an enlarged head), and/or mechanisms that include a snap        ring or analogous structure. The disclosed mechanisms permit        reliable mounting of a ball/sphere relative to a pedicle screw.    -   Devices, systems and methods that provide dynamic spine        stabilization systems/implementations over a single level and/or        multiple levels, including single and multi-level systems that        permit one or more adjustments to be made (e.g., in situ and/or        prior to clinical installation), e.g., adjustments as to the        magnitude and/or displacement-response characteristics of the        forces applied by the stabilization system.    -   Devices, systems and methods that provide multi-level dynamic        stabilization systems that include different stabilization        modalities at different levels, e.g., at least one level        including a dynamic stabilizing member and at least one level        including a non-dynamic stabilizing member. According to        exemplary embodiments of mixed multi-level stabilization        systems, the dynamic and non-dynamic stabilizing elements are        mounted with respect to common, i.e., identical, pedicle screws        as disclosed herein.    -   Devices, systems and methods that provide or utilize        advantageous installation accessories (e.g., cone structures)        for facilitating placement and/or installation of spine        stabilization system components, such accessories being        particularly adapted for use with a conventional guidewires to        facilitate alignment/positioning of system components relative        to the pedicle screw.    -   Devices, systems and methods that provide or utilize dynamic        spring stabilization components that include a cover and/or        sheath structure that provides advantageous protection to inner        force-imparting component(s) while exhibiting clinically        acceptable interaction with surrounding anatomical fluids and/or        structures, e.g., a cover and/or sheath structure that is        fabricated (in whole or in part) from ePTFE, UHMWPE and/or        alternative polymeric materials such as        polycarbonate-polyurethane copolymers and/or blends.    -   Devices, systems and methods that provide advantageous dynamic        spine stabilization connection systems that facilitate        substantially rigid attachment of an elongated member (e.g., a        rod) relative to the pedicle screw while simultaneously        facilitating movement relative to adjacent structures (e.g., an        adjacent pedicle screw) to permit easy and efficacious        intra-operative system placement;    -   Devices, systems and methods that provide an advantageous        “pre-load” arrangement for a securing structure (e.g., a set        screw) that may be used in situ to mount a ball joint relative        to a pedicle screw, thereby minimizing the potential for        clinical difficulties associated with location and/or alignment        of such securing structure(s).    -   Devices, systems and methods that embody or utilize advantageous        kits that include an enclosure and necessary components for        implementing dynamic spine stabilization in the manner described        herein, such enclosure/components being supplied in a clinically        acceptable form (e.g., sterilized for clinical use).

Although the present disclosure has been disclosed with reference toexemplary embodiments and implementations thereof, those skilled in theart will appreciate that the present disclosure is susceptible tovarious modifications, refinements and/or implementations withoutdeparting from the spirit or scope of the present invention. In fact, itis contemplated the disclosed connection structure may be employed in avariety of environments and clinical settings without departing from thespirit or scope of the present invention. Accordingly, while exemplaryembodiments of the present disclosure have been shown and described, itwill be understood that there is no intent to limit the invention bysuch disclosure, but rather, the present invention is intended to coverand encompass all modifications and alternate constructions fallingwithin the spirit and scope hereof.

The invention claimed is:
 1. A method for stabilizing a spinal segment,comprising: (a) introducing a first pedicle screw into a first pedicleof a spine; (b) introducing a second pedicle screw into a second pedicleof the spine; (c) providing a dynamic stabilization device, including:(i) a dynamic stabilizing member, (ii) a first dynamic junction foroperative association with a first end of the dynamic stabilizingmember, and (iii) a second dynamic junction for operative associationwith a second end of the dynamic stabilizing member; (d) mounting thefirst dynamic junction of the dynamic stabilization device with respectto the first pedicle screw; and (e) mounting the second dynamic junctionof the dynamic stabilization device with respect to the second pediclescrew, wherein each of the first and second dynamic junctions supportsthree degrees of rotational freedom; wherein the dynamic stabilizationdevice enables and provides resistance to relative movement between thefirst and second pedicles in a first axis; and wherein the dynamicstabilizing member exhibits a variable spring rate that is greater whenthe spine is within a neutral zone than when the spine is outside of theneutral zone.
 2. The method of claim 1, wherein the first and seconddynamic junctions are ball joints.
 3. The method of claim 2, wherein thefirst dynamic junction includes a first socket member securable relativeto the first end of the dynamic stabilizing member and a first sphericalelement positioned within the first socket member, and wherein thesecond dynamic junction includes a second socket member securablerelative to the second end of the dynamic stabilizing member and asecond spherical element positioned within the second socket member. 4.The method of claim 3, wherein the first socket member defines a firstrace for rotationally associating with the first spherical element, andwherein the second socket member defines a second race for rotationallyassociating with the second spherical element.
 5. The method of claim 4,wherein the first race include a first pair of slots for introducing thefirst spherical element, and wherein the second race includes a secondpair of slots for introducing the second spherical element.
 6. Themethod of claim 3, wherein the first spherical element engages the firstsocket at or near a plane that defines the diameter of the firstspherical element, and wherein the second spherical element engages thesecond socket at or near a plane that defines the diameter of the secondspherical element.
 7. The method of claim 1, wherein the first sphericalelement defines a first aperture for receiving a first upwardlyextending structure of the first pedicle screw, and wherein the secondspherical element defines a second aperture for receiving a secondupwardly extending structure of the second pedicle screw, whereinmounting the first dynamic junction of the dynamic stabilization devicewith respect to the first pedicle screw includes receiving the firstupwardly extending structure within the first aperture, and whereinmounting the second dynamic junction of the dynamic stabilization devicewith respect to the second pedicle screw includes receiving the secondupwardly extending structure within the second aperture.
 8. The methodof claim 7, wherein mounting the first dynamic junction of the dynamicstabilization device with respect to the first pedicle screw furtherincludes securing the first upwardly extending structure within thefirst aperture, and wherein mounting the second dynamic junction of thedynamic stabilization device within the second pedicle screw includessecuring the second upwardly extending structure within the secondaperture.
 9. The method of claim 8, wherein a first snap-ring mechanismis used to secure the first upwardly extending structure within thefirst aperture, and wherein a second snap-ring mechanism is used tosecure the second upwardly extending structure within the secondaperture.
 10. The method of claim 8, wherein securing the first upwardlyextending structure within the first aperture includes deflecting aportion of the first upwardly extending structure, and wherein securingthe second upwardly extending structure within the second apertureincludes deflecting a portion of the second upwardly extendingstructure.
 11. The method of claim 1, wherein the first and seconddynamic junctions reduce torsional stress in the first and secondpedicle screws during relative movement between the first and secondpedicles.
 12. The method of claim 1, wherein the first and seconddynamic junctions reduce bending stress in the dynamic stabilizingmember.
 13. The method of claim 1, wherein the resistance is an elasticresistance.
 14. The method of claim 1, wherein the dynamic stabilizingmember exhibits a first spring rate when the spine is within a neutralzone and a second spring rate when the spine is outside of the neutralzone, wherein the first spring rate is greater than the second springrate.
 15. The method of claim 1, wherein the first dynamic junction ispositioned substantially along the first axis.
 16. The method of claim1, wherein the second dynamic junction is positioned substantially offthe first axis.
 17. The method of claim 1, wherein the first dynamicjunction is integrally formed with respect to the first end of thedynamic stabilizing member.
 18. The method of claim 1, wherein thesecond dynamic junction is separately formed with respect to the secondend of the dynamic stabilizing member.
 19. The method of claim 18,further comprising securing the second dynamic junction relative to thesecond end of the dynamic stabilizing member, before, during or aftermounting of the second dynamic junction.
 20. The method of claim 1,wherein a baseline distance is set based on the distance between thefirst and second pedicle screws after the first and second pediclescrews are introduced into the first and second pedicles.
 21. The methodof claim 1, wherein a baseline distance is set by selectively setting adistance between the dynamic stabilizing member and the second dynamicjunction.
 22. The method of claim 21, wherein the second dynamicjunction defines a connector configured for securing the dynamicstabilizing member relative to the second dynamic junction so as to setthe distance between the dynamic stabilizing member and the seconddynamic junction.
 23. The method of claim 22, wherein the connector is arod connector defining a traverse aperture for receiving a rod extendingfrom the dynamic stabilizing member, wherein the rod connector isconfigured for securing the rod at a selected position within theaperture thereby setting the distance between the dynamic stabilizingmember and the second dynamic junction.
 24. The method of claim 23,further comprising selecting the length of the rod extending from thedynamic stabilizing member, by at least one of (i) adjusting the lengthof the rod, and (ii) initially selecting a rod of appropriate length.25. A method for stabilizing a spinal segment, comprising: (a)introducing a first pedicle screw into a first pedicle of a spine; (b)introducing a second pedicle screw into a second pedicle of the spine;(c) providing a dynamic stabilization device, including: (i) a dynamicstabilizing member, (ii) a first dynamic junction for operativeassociation with a first end of the dynamic stabilizing member, and(iii) a second dynamic junction for operative association with a secondend of the dynamic stabilizing member; (d) mounting the first dynamicjunction of the dynamic stabilization device with respect to the firstpedicle screw; and (e) mounting the second dynamic junction of thedynamic stabilization device with respect to the second pedicle screw,wherein each of the first and second dynamic junctions supports threedegrees of rotational freedom; wherein the dynamic stabilization deviceenables relative movement between the first and second pedicles; whereinthe first spherical element defines a first aperture for receiving afirst upwardly extending structure of the first pedicle screw, andwherein the second spherical element defines a second aperture forreceiving a second upwardly extending structure of the second pediclescrew; and wherein mounting the first dynamic junction of the dynamicstabilization device with respect to the first pedicle screw includesreceiving and securing the first upwardly extending structure within thefirst aperture, and wherein mounting the second dynamic junction of thedynamic stabilization device with respect to the second pedicle screwincludes receiving and securing the second upwardly extending structurewithin the second aperture; wherein a first snap-ring mechanism is usedto secure the first upwardly extending structure within the firstaperture, and wherein a second snap-ring mechanism is used to secure thesecond upwardly extending structure within the second aperture.
 26. Amethod for stabilizing a spinal segment, comprising: (a) introducing afirst pedicle screw into a first pedicle of a spine; (b) introducing asecond pedicle screw into a second pedicle of the spine; (c) providing adynamic stabilization device, including: (i) a dynamic stabilizingmember, (ii) a first dynamic junction for operative association with afirst end of the dynamic stabilizing member, and (iii) a second dynamicjunction for operative association with a second end of the dynamicstabilizing member; (d) mounting the first dynamic junction of thedynamic stabilization device with respect to the first pedicle screw;and (e) mounting the second dynamic junction of the dynamicstabilization device with respect to the second pedicle screw, whereineach of the first and second dynamic junctions supports three degrees ofrotational freedom; wherein the dynamic stabilization device enablesrelative movement between the first and second pedicles; wherein thefirst spherical element defines a first aperture for receiving a firstupwardly extending structure of the first pedicle screw, and wherein thesecond spherical element defines a second aperture for receiving asecond upwardly extending structure of the second pedicle screw; andwherein mounting the first dynamic junction of the dynamic stabilizationdevice with respect to the first pedicle screw includes receiving andsecuring the first upwardly extending structure within the firstaperture, and wherein mounting the second dynamic junction of thedynamic stabilization device with respect to the second pedicle screwincludes receiving and securing the second upwardly extending structurewithin the second aperture; wherein securing the first upwardlyextending structure within the first aperture includes deflecting aportion of the first upwardly extending structure, and wherein securingthe second upwardly extending structure within the second apertureincludes deflecting a portion of the second upwardly extendingstructure.
 27. A method for stabilizing a spinal segment, comprising:(a) introducing a first pedicle screw into a first pedicle of a spine;(b) introducing a second pedicle screw into a second pedicle of thespine; (c) providing a dynamic stabilization device, including: (i) adynamic stabilizing member, (ii) a first dynamic junction for operativeassociation with a first end of the dynamic stabilizing member, and(iii) a second dynamic junction for operative association with a secondend of the dynamic stabilizing member; (d) mounting the first dynamicjunction of the dynamic stabilization device with respect to the firstpedicle screw; and (e) mounting the second dynamic junction of thedynamic stabilization device with respect to the second pedicle screw,wherein each of the first and second dynamic junctions supports threedegrees of rotational freedom; wherein the dynamic stabilization deviceenables relative movement between the first and second pedicles; andwherein the dynamic stabilizing member provides resistance to movementbetween the first and second pedicles in a first axis, wherein thesecond dynamic junctions is positioned substantially off the first axis.